Ignore:
Timestamp:
20/01/14 07:43:53 (8 years ago)
Author:
julian.reschke@…
Message:

update rfc2617.xml (ABNF alignment was off from published version), regen all HTML

File:
1 edited

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  • draft-ietf-httpbis/orig/rfc2965.html

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    346334      <link rel="Help" title="RFC-Editor's Status Page" href="http://www.rfc-editor.org/info/rfc2965">
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    383371      </table>
    384372      <p class="title">HTTP State Management Mechanism</p>
    385       <h1><a id="rfc.status" href="#rfc.status">Status of this Memo</a></h1>
    386       <p>This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions
    387          for improvements. Please refer to the current edition of the “Internet Official Protocol Standards” (STD 1) for the standardization
    388          state and status of this protocol. Distribution of this memo is unlimited.
    389       </p>
    390       <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
    391       <p>Copyright © The Internet Society (2000). All Rights Reserved.</p>
    392       <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1>
     373      <div id="rfc.status">
     374         <h1><a href="#rfc.status">Status of this Memo</a></h1>
     375         <p>This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions
     376            for improvements. Please refer to the current edition of the “Internet Official Protocol Standards” (STD 1) for the standardization
     377            state and status of this protocol. Distribution of this memo is unlimited.
     378         </p>
     379      </div>
     380      <div id="rfc.copyrightnotice">
     381         <h1><a href="#rfc.copyrightnotice">Copyright Notice</a></h1>
     382         <p>Copyright © The Internet Society (2000). All Rights Reserved.</p>
     383      </div>
     384      <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1>
    393385      <p>This document specifies a way to create a stateful session with Hypertext Transfer Protocol (HTTP) requests and responses.
    394386         It describes three new headers, Cookie, Cookie2, and Set-Cookie2, which carry state information between participating origin
    395387         servers and user agents. The method described here differs from Netscape's Cookie proposal <a href="#Netscape" id="rfc.xref.Netscape.1"><cite title="Persistent Client State -- HTTP Cookies">[Netscape]</cite></a>, but it can interoperate with HTTP/1.0 user agents that use Netscape's method. (See the HISTORICAL section.)
    396388      </p>
    397       <p>This document reflects implementation experience with RFC 2109 and obsoletes it.</p> 
     389      <p>This document reflects implementation experience with RFC 2109 and obsoletes it.</p>
    398390      <hr class="noprint">
    399391      <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1>
    400392      <ul class="toc">
    401          <li>1.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.1">TERMINOLOGY</a><ul>
    402                <li>1.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.1.1">Requirements</a></li>
     393         <li><a href="#rfc.section.1">1.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.1">TERMINOLOGY</a><ul>
     394               <li><a href="#rfc.section.1.1">1.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.1.1">Requirements</a></li>
    403395            </ul>
    404396         </li>
    405          <li>2.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.2">STATE AND SESSIONS</a></li>
    406          <li>3.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3">DESCRIPTION</a><ul>
    407                <li>3.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.1">Syntax: General</a></li>
    408                <li>3.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.2">Origin Server Role</a><ul>
    409                      <li>3.2.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.2.1">General</a></li>
    410                      <li>3.2.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.2.2">Set-Cookie2 Syntax</a></li>
    411                      <li>3.2.3&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.2.3">Controlling Caching</a></li>
     397         <li><a href="#rfc.section.2">2.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.2">STATE AND SESSIONS</a></li>
     398         <li><a href="#rfc.section.3">3.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3">DESCRIPTION</a><ul>
     399               <li><a href="#rfc.section.3.1">3.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.1">Syntax: General</a></li>
     400               <li><a href="#rfc.section.3.2">3.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.2">Origin Server Role</a><ul>
     401                     <li><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.2.1">General</a></li>
     402                     <li><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.2.2">Set-Cookie2 Syntax</a></li>
     403                     <li><a href="#rfc.section.3.2.3">3.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.2.3">Controlling Caching</a></li>
    412404                  </ul>
    413405               </li>
    414                <li>3.3&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3">User Agent Role</a><ul>
    415                      <li>3.3.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3.1">Interpreting Set-Cookie2</a></li>
    416                      <li>3.3.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3.2">Rejecting Cookies</a></li>
    417                      <li>3.3.3&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3.3">Cookie Management</a></li>
    418                      <li>3.3.4&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3.4">Sending Cookies to the Origin Server</a></li>
    419                      <li>3.3.5&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3.5">Identifying What Version is Understood:  Cookie2</a></li>
    420                      <li>3.3.6&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3.6">Sending Cookies in Unverifiable Transactions</a></li>
     406               <li><a href="#rfc.section.3.3">3.3</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3">User Agent Role</a><ul>
     407                     <li><a href="#rfc.section.3.3.1">3.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3.1">Interpreting Set-Cookie2</a></li>
     408                     <li><a href="#rfc.section.3.3.2">3.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3.2">Rejecting Cookies</a></li>
     409                     <li><a href="#rfc.section.3.3.3">3.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3.3">Cookie Management</a></li>
     410                     <li><a href="#rfc.section.3.3.4">3.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3.4">Sending Cookies to the Origin Server</a></li>
     411                     <li><a href="#rfc.section.3.3.5">3.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3.5">Identifying What Version is Understood:  Cookie2</a></li>
     412                     <li><a href="#rfc.section.3.3.6">3.3.6</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.3.6">Sending Cookies in Unverifiable Transactions</a></li>
    421413                  </ul>
    422414               </li>
    423                <li>3.4&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.4">How an Origin Server Interprets the Cookie Header</a></li>
    424                <li>3.5&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.5">Caching Proxy Role</a></li>
     415               <li><a href="#rfc.section.3.4">3.4</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.4">How an Origin Server Interprets the Cookie Header</a></li>
     416               <li><a href="#rfc.section.3.5">3.5</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.5">Caching Proxy Role</a></li>
    425417            </ul>
    426418         </li>
    427          <li>4.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.4">EXAMPLES</a><ul>
    428                <li>4.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.4.1">Example 1</a></li>
    429                <li>4.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.4.2">Example 2</a></li>
     419         <li><a href="#rfc.section.4">4.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.4">EXAMPLES</a><ul>
     420               <li><a href="#rfc.section.4.1">4.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.4.1">Example 1</a></li>
     421               <li><a href="#rfc.section.4.2">4.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.4.2">Example 2</a></li>
    430422            </ul>
    431423         </li>
    432          <li>5.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.5">IMPLEMENTATION CONSIDERATIONS</a><ul>
    433                <li>5.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.5.1">Set-Cookie2 Content</a></li>
    434                <li>5.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.5.2">Stateless Pages</a></li>
    435                <li>5.3&nbsp;&nbsp;&nbsp;<a href="#rfc.section.5.3">Implementation Limits</a><ul>
    436                      <li>5.3.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.5.3.1">Denial of Service Attacks</a></li>
     424         <li><a href="#rfc.section.5">5.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.5">IMPLEMENTATION CONSIDERATIONS</a><ul>
     425               <li><a href="#rfc.section.5.1">5.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.5.1">Set-Cookie2 Content</a></li>
     426               <li><a href="#rfc.section.5.2">5.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.5.2">Stateless Pages</a></li>
     427               <li><a href="#rfc.section.5.3">5.3</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.5.3">Implementation Limits</a><ul>
     428                     <li><a href="#rfc.section.5.3.1">5.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.5.3.1">Denial of Service Attacks</a></li>
    437429                  </ul>
    438430               </li>
    439431            </ul>
    440432         </li>
    441          <li>6.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.6">PRIVACY</a><ul>
    442                <li>6.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.6.1">User Agent Control</a></li>
    443                <li>6.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.6.2">Origin Server Role</a></li>
    444                <li>6.3&nbsp;&nbsp;&nbsp;<a href="#rfc.section.6.3">Clear Text</a></li>
     433         <li><a href="#rfc.section.6">6.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.6">PRIVACY</a><ul>
     434               <li><a href="#rfc.section.6.1">6.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.6.1">User Agent Control</a></li>
     435               <li><a href="#rfc.section.6.2">6.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.6.2">Origin Server Role</a></li>
     436               <li><a href="#rfc.section.6.3">6.3</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.6.3">Clear Text</a></li>
    445437            </ul>
    446438         </li>
    447          <li>7.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.7">SECURITY CONSIDERATIONS</a><ul>
    448                <li>7.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.7.1">Protocol Design</a></li>
    449                <li>7.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.7.2">Cookie Spoofing</a></li>
    450                <li>7.3&nbsp;&nbsp;&nbsp;<a href="#rfc.section.7.3">Unexpected Cookie Sharing</a></li>
    451                <li>7.4&nbsp;&nbsp;&nbsp;<a href="#rfc.section.7.4">Cookies For Account Information</a></li>
     439         <li><a href="#rfc.section.7">7.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.7">SECURITY CONSIDERATIONS</a><ul>
     440               <li><a href="#rfc.section.7.1">7.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.7.1">Protocol Design</a></li>
     441               <li><a href="#rfc.section.7.2">7.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.7.2">Cookie Spoofing</a></li>
     442               <li><a href="#rfc.section.7.3">7.3</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.7.3">Unexpected Cookie Sharing</a></li>
     443               <li><a href="#rfc.section.7.4">7.4</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.7.4">Cookies For Account Information</a></li>
    452444            </ul>
    453445         </li>
    454          <li>8.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.8">OTHER, SIMILAR, PROPOSALS</a></li>
    455          <li>9.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.9">HISTORICAL</a><ul>
    456                <li>9.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.9.1">Compatibility with Existing Implementations</a></li>
    457                <li>9.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.9.2">Caching and HTTP/1.0</a></li>
     446         <li><a href="#rfc.section.8">8.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.8">OTHER, SIMILAR, PROPOSALS</a></li>
     447         <li><a href="#rfc.section.9">9.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.9">HISTORICAL</a><ul>
     448               <li><a href="#rfc.section.9.1">9.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.9.1">Compatibility with Existing Implementations</a></li>
     449               <li><a href="#rfc.section.9.2">9.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.9.2">Caching and HTTP/1.0</a></li>
    458450            </ul>
    459451         </li>
    460          <li>10.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.10">ACKNOWLEDGEMENTS</a></li>
    461          <li>11.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a></li>
     452         <li><a href="#rfc.section.10">10.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.10">ACKNOWLEDGEMENTS</a></li>
     453         <li><a href="#rfc.section.11">11.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a></li>
    462454         <li><a href="#rfc.authors">Authors' Addresses</a></li>
    463455         <li><a href="#rfc.index">Index</a></li>
     
    465457      </ul>
    466458      <hr class="noprint">
    467       <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;TERMINOLOGY
    468       </h1>
    469       <p id="rfc.section.1.p.1">The terms user agent, client, server, proxy, origin server, and http_URL have the same meaning as in the HTTP/1.1 specification <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. The terms abs_path and absoluteURI have the same meaning as in the URI Syntax specification <a href="#RFC2396" id="rfc.xref.RFC2396.1"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>.
    470       </p>
    471       <p id="rfc.section.1.p.2">Host name (HN) means either the host domain name (HDN) or the numeric Internet Protocol (IP) address of a host. The fully
    472          qualified domain name is preferred; use of numeric IP addresses is strongly discouraged.
    473       </p>
    474       <p id="rfc.section.1.p.3">The terms request-host and request-URI refer to the values the client would send to the server as, respectively, the host
    475          (but not port) and abs_path portions of the absoluteURI (http_URL) of the HTTP request line. Note that request-host is a HN.
    476       </p>
    477       <p id="rfc.section.1.p.4">The term effective host name is related to host name. If a host name contains no dots, the effective host name is that name
    478          with the string .local appended to it. Otherwise the effective host name is the same as the host name. Note that all effective
    479          host names contain at least one dot.
    480       </p>
    481       <p id="rfc.section.1.p.5">The term request-port refers to the port portion of the absoluteURI (http_URL) of the HTTP request line. If the absoluteURI
    482          has no explicit port, the request-port is the HTTP default, 80. The request-port of a cookie is the request-port of the request
    483          in which a Set-Cookie2 response header was returned to the user agent.
    484       </p>
    485       <p id="rfc.section.1.p.6">Host names can be specified either as an IP address or a HDN string. Sometimes we compare one host name with another. (Such
    486          comparisons <em class="bcp14">SHALL</em> be case-insensitive.) Host A's name domain-matches host B's if
    487       </p>
    488       <ul>
    489          <li>their host name strings string-compare equal; or</li>
    490          <li>A is a HDN string and has the form NB, where N is a non-empty name string, B has the form .B', and B' is a HDN string. (So,
    491             x.y.com domain-matches .Y.com but not Y.com.)
    492          </li>
    493       </ul>
    494       <p id="rfc.section.1.p.7">Note that domain-match is not a commutative operation: a.b.c.com domain-matches .c.com, but not the reverse.</p>
    495       <p id="rfc.section.1.p.8">The reach R of a host name H is defined as follows: </p>
    496       <ul>
    497          <li>If
    498             <ul>
    499                <li>H is the host domain name of a host; and,</li>
    500                <li>H has the form A.B; and</li>
    501                <li>A has no embedded (that is, interior) dots; and</li>
    502                <li>B has at least one embedded dot, or B is the string "local". then the reach of H is .B.</li>
    503             </ul>
    504          </li>
    505          <li>Otherwise, the reach of H is H.</li>
    506       </ul>
    507       <p id="rfc.section.1.p.9">For two strings that represent paths, P1 and P2, P1 path-matches P2 if P2 is a prefix of P1 (including the case where P1 and
    508          P2 string- compare equal). Thus, the string /tec/waldo path-matches /tec.
    509       </p>
    510       <p id="rfc.section.1.p.10">Because it was used in Netscape's original implementation of state management, we will use the term cookie to refer to the
    511          state information that passes between an origin server and user agent, and that gets stored by the user agent.
    512       </p>
    513       <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;Requirements
    514       </h2>
    515       <p id="rfc.section.1.1.p.1">The key words "MAY", "MUST", "MUST NOT", "OPTIONAL", "RECOMMENDED", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT"
    516          in this document are to be interpreted as described in RFC 2119 <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.
    517       </p>
     459      <div>
     460         <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;TERMINOLOGY
     461         </h1>
     462         <p id="rfc.section.1.p.1">The terms user agent, client, server, proxy, origin server, and http_URL have the same meaning as in the HTTP/1.1 specification <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. The terms abs_path and absoluteURI have the same meaning as in the URI Syntax specification <a href="#RFC2396" id="rfc.xref.RFC2396.1"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>.
     463         </p>
     464         <p id="rfc.section.1.p.2">Host name (HN) means either the host domain name (HDN) or the numeric Internet Protocol (IP) address of a host. The fully
     465            qualified domain name is preferred; use of numeric IP addresses is strongly discouraged.
     466         </p>
     467         <p id="rfc.section.1.p.3">The terms request-host and request-URI refer to the values the client would send to the server as, respectively, the host
     468            (but not port) and abs_path portions of the absoluteURI (http_URL) of the HTTP request line. Note that request-host is a HN.
     469         </p>
     470         <p id="rfc.section.1.p.4">The term effective host name is related to host name. If a host name contains no dots, the effective host name is that name
     471            with the string .local appended to it. Otherwise the effective host name is the same as the host name. Note that all effective
     472            host names contain at least one dot.
     473         </p>
     474         <p id="rfc.section.1.p.5">The term request-port refers to the port portion of the absoluteURI (http_URL) of the HTTP request line. If the absoluteURI
     475            has no explicit port, the request-port is the HTTP default, 80. The request-port of a cookie is the request-port of the request
     476            in which a Set-Cookie2 response header was returned to the user agent.
     477         </p>
     478         <p id="rfc.section.1.p.6">Host names can be specified either as an IP address or a HDN string. Sometimes we compare one host name with another. (Such
     479            comparisons <em class="bcp14">SHALL</em> be case-insensitive.) Host A's name domain-matches host B's if
     480         </p>
     481         <ul>
     482            <li>their host name strings string-compare equal; or</li>
     483            <li>A is a HDN string and has the form NB, where N is a non-empty name string, B has the form .B', and B' is a HDN string. (So,
     484               x.y.com domain-matches .Y.com but not Y.com.)
     485            </li>
     486         </ul>
     487         <p id="rfc.section.1.p.7">Note that domain-match is not a commutative operation: a.b.c.com domain-matches .c.com, but not the reverse.</p>
     488         <p id="rfc.section.1.p.8">The reach R of a host name H is defined as follows: </p>
     489         <ul>
     490            <li>If
     491               <ul>
     492                  <li>H is the host domain name of a host; and,</li>
     493                  <li>H has the form A.B; and</li>
     494                  <li>A has no embedded (that is, interior) dots; and</li>
     495                  <li>B has at least one embedded dot, or B is the string "local". then the reach of H is .B.</li>
     496               </ul>
     497            </li>
     498            <li>Otherwise, the reach of H is H.</li>
     499         </ul>
     500         <p id="rfc.section.1.p.9">For two strings that represent paths, P1 and P2, P1 path-matches P2 if P2 is a prefix of P1 (including the case where P1 and
     501            P2 string- compare equal). Thus, the string /tec/waldo path-matches /tec.
     502         </p>
     503         <p id="rfc.section.1.p.10">Because it was used in Netscape's original implementation of state management, we will use the term cookie to refer to the
     504            state information that passes between an origin server and user agent, and that gets stored by the user agent.
     505         </p>
     506         <div>
     507            <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;Requirements
     508            </h2>
     509            <p id="rfc.section.1.1.p.1">The key words "MAY", "MUST", "MUST NOT", "OPTIONAL", "RECOMMENDED", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT"
     510               in this document are to be interpreted as described in RFC 2119 <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.
     511            </p>
     512         </div>
     513      </div>
    518514      <hr class="noprint">
    519       <h1 id="rfc.section.2" class="np"><a href="#rfc.section.2">2.</a>&nbsp;STATE AND SESSIONS
    520       </h1>
    521       <p id="rfc.section.2.p.1">This document describes a way to create stateful sessions with HTTP requests and responses. Currently, HTTP servers respond
    522          to each client request without relating that request to previous or subsequent requests; the state management mechanism allows
    523          clients and servers that wish to exchange state information to place HTTP requests and responses within a larger context,
    524          which we term a "session". This context might be used to create, for example, a "shopping cart", in which user selections
    525          can be aggregated before purchase, or a magazine browsing system, in which a user's previous reading affects which offerings
    526          are presented.
    527       </p>
    528       <p id="rfc.section.2.p.2">Neither clients nor servers are required to support cookies. A server <em class="bcp14">MAY</em> refuse to provide content to a client that does not return the cookies it sends.
    529       </p>
     515      <div>
     516         <h1 id="rfc.section.2" class="np"><a href="#rfc.section.2">2.</a>&nbsp;STATE AND SESSIONS
     517         </h1>
     518         <p id="rfc.section.2.p.1">This document describes a way to create stateful sessions with HTTP requests and responses. Currently, HTTP servers respond
     519            to each client request without relating that request to previous or subsequent requests; the state management mechanism allows
     520            clients and servers that wish to exchange state information to place HTTP requests and responses within a larger context,
     521            which we term a "session". This context might be used to create, for example, a "shopping cart", in which user selections
     522            can be aggregated before purchase, or a magazine browsing system, in which a user's previous reading affects which offerings
     523            are presented.
     524         </p>
     525         <p id="rfc.section.2.p.2">Neither clients nor servers are required to support cookies. A server <em class="bcp14">MAY</em> refuse to provide content to a client that does not return the cookies it sends.
     526         </p>
     527      </div>
    530528      <hr class="noprint">
    531       <h1 id="rfc.section.3" class="np"><a href="#rfc.section.3">3.</a>&nbsp;DESCRIPTION
    532       </h1>
    533       <p id="rfc.section.3.p.1">We describe here a way for an origin server to send state information to the user agent, and for the user agent to return
    534          the state information to the origin server. The goal is to have a minimal impact on HTTP and user agents.
    535       </p>
    536       <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;Syntax: General
    537       </h2>
    538       <p id="rfc.section.3.1.p.1">The two state management headers, Set-Cookie2 and Cookie, have common syntactic properties involving attribute-value pairs.
    539          The following grammar uses the notation, and tokens DIGIT (decimal digits), token (informally, a sequence of non-special,
    540          non-white space characters), and http_URL from the HTTP/1.1 specification <a href="#RFC2616" id="rfc.xref.RFC2616.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a> to describe their syntax.
    541       </p>
    542       <div id="rfc.figure.u.1"></div><pre class="inline">
     529      <div>
     530         <h1 id="rfc.section.3" class="np"><a href="#rfc.section.3">3.</a>&nbsp;DESCRIPTION
     531         </h1>
     532         <p id="rfc.section.3.p.1">We describe here a way for an origin server to send state information to the user agent, and for the user agent to return
     533            the state information to the origin server. The goal is to have a minimal impact on HTTP and user agents.
     534         </p>
     535         <div>
     536            <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;Syntax: General
     537            </h2>
     538            <p id="rfc.section.3.1.p.1">The two state management headers, Set-Cookie2 and Cookie, have common syntactic properties involving attribute-value pairs.
     539               The following grammar uses the notation, and tokens DIGIT (decimal digits), token (informally, a sequence of non-special,
     540               non-white space characters), and http_URL from the HTTP/1.1 specification <a href="#RFC2616" id="rfc.xref.RFC2616.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a> to describe their syntax.
     541            </p>
     542            <div id="rfc.figure.u.1"></div><pre class="inline">
    543543   av-pairs    =     av-pair *(";" av-pair)
    544544   av-pair     =     attr ["=" value]              ; optional value
     
    546546   value       =     token | quoted-string
    547547</pre><p id="rfc.section.3.1.p.3">Attributes (names) (attr) are case-insensitive. White space is permitted between tokens. Note that while the above syntax
    548          description shows value as optional, most attrs require them.
    549       </p>
    550       <p id="rfc.section.3.1.p.4">NOTE: The syntax above allows whitespace between the attribute and the = sign.</p>
    551       <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;Origin Server Role
    552       </h2>
    553       <h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;General
    554       </h3>
    555       <p id="rfc.section.3.2.1.p.1">The origin server initiates a session, if it so desires. To do so, it returns an extra response header to the client, Set-Cookie2.
    556          (The details follow later.)
    557       </p>
    558       <p id="rfc.section.3.2.1.p.2">A user agent returns a Cookie request header (see below) to the origin server if it chooses to continue a session. The origin
    559          server <em class="bcp14">MAY</em> ignore it or use it to determine the current state of the session. It <em class="bcp14">MAY</em> send back to the client a Set-Cookie2 response header with the same or different information, or it <em class="bcp14">MAY</em> send no Set-Cookie2 header at all. The origin server effectively ends a session by sending the client a Set-Cookie2 header
    560          with Max-Age=0.
    561       </p>
    562       <p id="rfc.section.3.2.1.p.3">Servers <em class="bcp14">MAY</em> return Set-Cookie2 response headers with any response. User agents <em class="bcp14">SHOULD</em> send Cookie request headers, subject to other rules detailed below, with every request.
    563       </p>
    564       <p id="rfc.section.3.2.1.p.4">An origin server <em class="bcp14">MAY</em> include multiple Set-Cookie2 headers in a response. Note that an intervening gateway could fold multiple such headers into
    565          a single header.
    566       </p>
    567       <div id="rfc.iref.s.1"></div>
    568       <div id="rfc.iref.h.1"></div>
    569       <h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;Set-Cookie2 Syntax
    570       </h3>
    571       <p id="rfc.section.3.2.2.p.1">The syntax for the Set-Cookie2 response header is</p>
    572       <div id="rfc.figure.u.2"></div><pre class="inline">
     548               description shows value as optional, most attrs require them.
     549            </p>
     550            <p id="rfc.section.3.1.p.4">NOTE: The syntax above allows whitespace between the attribute and the = sign.</p>
     551         </div>
     552         <div>
     553            <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;Origin Server Role
     554            </h2>
     555            <div>
     556               <h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;General
     557               </h3>
     558               <p id="rfc.section.3.2.1.p.1">The origin server initiates a session, if it so desires. To do so, it returns an extra response header to the client, Set-Cookie2.
     559                  (The details follow later.)
     560               </p>
     561               <p id="rfc.section.3.2.1.p.2">A user agent returns a Cookie request header (see below) to the origin server if it chooses to continue a session. The origin
     562                  server <em class="bcp14">MAY</em> ignore it or use it to determine the current state of the session. It <em class="bcp14">MAY</em> send back to the client a Set-Cookie2 response header with the same or different information, or it <em class="bcp14">MAY</em> send no Set-Cookie2 header at all. The origin server effectively ends a session by sending the client a Set-Cookie2 header
     563                  with Max-Age=0.
     564               </p>
     565               <p id="rfc.section.3.2.1.p.3">Servers <em class="bcp14">MAY</em> return Set-Cookie2 response headers with any response. User agents <em class="bcp14">SHOULD</em> send Cookie request headers, subject to other rules detailed below, with every request.
     566               </p>
     567               <p id="rfc.section.3.2.1.p.4">An origin server <em class="bcp14">MAY</em> include multiple Set-Cookie2 headers in a response. Note that an intervening gateway could fold multiple such headers into
     568                  a single header.
     569               </p>
     570            </div>
     571            <div>
     572               <div id="rfc.iref.s.1"></div>
     573               <div id="rfc.iref.h.1"></div>
     574               <h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;Set-Cookie2 Syntax
     575               </h3>
     576               <p id="rfc.section.3.2.2.p.1">The syntax for the Set-Cookie2 response header is</p>
     577               <div id="rfc.figure.u.2"></div><pre class="inline">
    573578   set-cookie      =       "Set-Cookie2:" cookies
    574579   cookies         =       1#cookie
     
    588593   portnum         =       1*DIGIT
    589594</pre><p id="rfc.section.3.2.2.p.3">Informally, the Set-Cookie2 response header comprises the token Set-Cookie2:, followed by a comma-separated list of one or
    590          more cookies. Each cookie begins with a NAME=VALUE pair, followed by zero or more semi-colon-separated attribute-value pairs.
    591          The syntax for attribute-value pairs was shown earlier. The specific attributes and the semantics of their values follows.
    592          The NAME=VALUE attribute-value pair <em class="bcp14">MUST</em> come first in each cookie. The others, if present, can occur in any order. If an attribute appears more than once in a cookie,
    593          the client <em class="bcp14">SHALL</em> use only the value associated with the first appearance of the attribute; a client <em class="bcp14">MUST</em> ignore values after the first.
    594       </p>
    595       <p id="rfc.section.3.2.2.p.4">The NAME of a cookie <em class="bcp14">MAY</em> be the same as one of the attributes in this specification. However, because the cookie's NAME must come first in a Set-Cookie2
    596          response header, the NAME and its VALUE cannot be confused with an attribute-value pair.
    597       </p>
    598       <p id="rfc.section.3.2.2.p.5"> </p>
    599       <dl>
    600          <dt>NAME=VALUE</dt>
    601          <dd>
    602             <p> <em class="bcp14">REQUIRED</em>. The name of the state information ("cookie") is NAME, and its value is VALUE. NAMEs that begin with $ are reserved and <em class="bcp14">MUST NOT</em> be used by applications.
    603             </p>
    604             <p>The VALUE is opaque to the user agent and may be anything the origin server chooses to send, possibly in a server-selected
    605                printable ASCII encoding. "Opaque" implies that the content is of interest and relevance only to the origin server. The content
    606                may, in fact, be readable by anyone that examines the Set-Cookie2 header.
    607             </p>
    608          </dd>
    609          <dt>Comment=value</dt>
    610          <dd>
    611             <p> <em class="bcp14">OPTIONAL</em>. Because cookies can be used to derive or store private information about a user, the value of the Comment attribute allows
    612                an origin server to document how it intends to use the cookie. The user can inspect the information to decide whether to initiate
    613                or continue a session with this cookie. Characters in value <em class="bcp14">MUST</em> be in UTF-8 encoding. <a href="#RFC2279" id="rfc.xref.RFC2279.1"><cite title="UTF-8, a transformation format of ISO 10646">[RFC2279]</cite></a>
    614             </p>
    615          </dd>
    616          <dt>CommentURL="http_URL"</dt>
    617          <dd>
    618             <p> <em class="bcp14">OPTIONAL</em>. Because cookies can be used to derive or store private information about a user, the CommentURL attribute allows an origin
    619                server to document how it intends to use the cookie. The user can inspect the information identified by the URL to decide
    620                whether to initiate or continue a session with this cookie.
    621             </p>
    622          </dd>
    623          <dt>Discard</dt>
    624          <dd>
    625             <p> <em class="bcp14">OPTIONAL</em>. The Discard attribute instructs the user agent to discard the cookie unconditionally when the user agent terminates.
    626             </p>
    627          </dd>
    628          <dt>Domain=value</dt>
    629          <dd>
    630             <p> <em class="bcp14">OPTIONAL</em>. The value of the Domain attribute specifies the domain for which the cookie is valid. If an explicitly specified value does
    631                not start with a dot, the user agent supplies a leading dot.
    632             </p>
    633          </dd>
    634          <dt>Max-Age=value</dt>
    635          <dd>
    636             <p> <em class="bcp14">OPTIONAL</em>. The value of the Max-Age attribute is delta-seconds, the lifetime of the cookie in seconds, a decimal non-negative integer.
    637                To handle cached cookies correctly, a client <em class="bcp14">SHOULD</em> calculate the age of the cookie according to the age calculation rules in the HTTP/1.1 specification <a href="#RFC2616" id="rfc.xref.RFC2616.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. When the age is greater than delta-seconds seconds, the client <em class="bcp14">SHOULD</em> discard the cookie. A value of zero means the cookie <em class="bcp14">SHOULD</em> be discarded immediately.
    638             </p>
    639          </dd>
    640          <dt>Path=value</dt>
    641          <dd>
    642             <p> <em class="bcp14">OPTIONAL</em>. The value of the Path attribute specifies the subset of URLs on the origin server to which this cookie applies.
    643             </p>
    644          </dd>
    645          <dt>Port[="portlist"]</dt>
    646          <dd>
    647             <p> <em class="bcp14">OPTIONAL</em>. The Port attribute restricts the port to which a cookie may be returned in a Cookie request header. Note that the syntax
    648                REQUIREs quotes around the <em class="bcp14">OPTIONAL</em> portlist even if there is only one portnum in portlist.
    649             </p>
    650          </dd>
    651          <dt>Secure</dt>
    652          <dd>
    653             <p> <em class="bcp14">OPTIONAL</em>. The Secure attribute (with no value) directs the user agent to use only (unspecified) secure means to contact the origin
    654                server whenever it sends back this cookie, to protect the confidentially and authenticity of the information in the cookie.
    655             </p>
    656             <p>The user agent (possibly with user interaction) <em class="bcp14">MAY</em> determine what level of security it considers appropriate for "secure" cookies. The Secure attribute should be considered
    657                security advice from the server to the user agent, indicating that it is in the session's interest to protect the cookie contents.
    658                When it sends a "secure" cookie back to a server, the user agent <em class="bcp14">SHOULD</em> use no less than the same level of security as was used when it received the cookie from the server.
    659             </p>
    660          </dd>
    661          <dt>Version=value</dt>
    662          <dd>
    663             <p> <em class="bcp14">REQUIRED</em>. The value of the Version attribute, a decimal integer, identifies the version of the state management specification to which
    664                the cookie conforms. For this specification, Version=1 applies.
    665             </p>
    666          </dd>
    667       </dl>
    668       <h3 id="rfc.section.3.2.3"><a href="#rfc.section.3.2.3">3.2.3</a>&nbsp;Controlling Caching
    669       </h3>
    670       <p id="rfc.section.3.2.3.p.1">An origin server must be cognizant of the effect of possible caching of both the returned resource and the Set-Cookie2 header.
    671          Caching "public" documents is desirable. For example, if the origin server wants to use a public document such as a "front
    672          door" page as a sentinel to indicate the beginning of a session for which a Set-Cookie2 response header must be generated,
    673          the page <em class="bcp14">SHOULD</em> be stored in caches "pre-expired" so that the origin server will see further requests. "Private documents", for example those
    674          that contain information strictly private to a session, <em class="bcp14">SHOULD</em> NOT be cached in shared caches.
    675       </p>
    676       <p id="rfc.section.3.2.3.p.2">If the cookie is intended for use by a single user, the Set-Cookie2 header <em class="bcp14">SHOULD NOT</em> be cached. A Set-Cookie2 header that is intended to be shared by multiple users <em class="bcp14">MAY</em> be cached.
    677       </p>
    678       <p id="rfc.section.3.2.3.p.3">The origin server <em class="bcp14">SHOULD</em> send the following additional HTTP/1.1 response headers, depending on circumstances:
    679       </p>
    680       <ul>
    681          <li>To suppress caching of the Set-Cookie2 header:
    682             <div id="rfc.figure.u.3"></div><pre class="text">
     595                  more cookies. Each cookie begins with a NAME=VALUE pair, followed by zero or more semi-colon-separated attribute-value pairs.
     596                  The syntax for attribute-value pairs was shown earlier. The specific attributes and the semantics of their values follows.
     597                  The NAME=VALUE attribute-value pair <em class="bcp14">MUST</em> come first in each cookie. The others, if present, can occur in any order. If an attribute appears more than once in a cookie,
     598                  the client <em class="bcp14">SHALL</em> use only the value associated with the first appearance of the attribute; a client <em class="bcp14">MUST</em> ignore values after the first.
     599               </p>
     600               <p id="rfc.section.3.2.2.p.4">The NAME of a cookie <em class="bcp14">MAY</em> be the same as one of the attributes in this specification. However, because the cookie's NAME must come first in a Set-Cookie2
     601                  response header, the NAME and its VALUE cannot be confused with an attribute-value pair.
     602               </p>
     603               <p id="rfc.section.3.2.2.p.5"></p>
     604               <dl>
     605                  <dt>NAME=VALUE</dt>
     606                  <dd>
     607                     <p><em class="bcp14">REQUIRED</em>. The name of the state information ("cookie") is NAME, and its value is VALUE. NAMEs that begin with $ are reserved and <em class="bcp14">MUST NOT</em> be used by applications.
     608                     </p>
     609                     <p>The VALUE is opaque to the user agent and may be anything the origin server chooses to send, possibly in a server-selected
     610                        printable ASCII encoding. "Opaque" implies that the content is of interest and relevance only to the origin server. The content
     611                        may, in fact, be readable by anyone that examines the Set-Cookie2 header.
     612                     </p>
     613                  </dd>
     614                  <dt>Comment=value</dt>
     615                  <dd>
     616                     <p><em class="bcp14">OPTIONAL</em>. Because cookies can be used to derive or store private information about a user, the value of the Comment attribute allows
     617                        an origin server to document how it intends to use the cookie. The user can inspect the information to decide whether to initiate
     618                        or continue a session with this cookie. Characters in value <em class="bcp14">MUST</em> be in UTF-8 encoding. <a href="#RFC2279" id="rfc.xref.RFC2279.1"><cite title="UTF-8, a transformation format of ISO 10646">[RFC2279]</cite></a>
     619                     </p>
     620                  </dd>
     621                  <dt>CommentURL="http_URL"</dt>
     622                  <dd>
     623                     <p><em class="bcp14">OPTIONAL</em>. Because cookies can be used to derive or store private information about a user, the CommentURL attribute allows an origin
     624                        server to document how it intends to use the cookie. The user can inspect the information identified by the URL to decide
     625                        whether to initiate or continue a session with this cookie.
     626                     </p>
     627                  </dd>
     628                  <dt>Discard</dt>
     629                  <dd>
     630                     <p><em class="bcp14">OPTIONAL</em>. The Discard attribute instructs the user agent to discard the cookie unconditionally when the user agent terminates.
     631                     </p>
     632                  </dd>
     633                  <dt>Domain=value</dt>
     634                  <dd>
     635                     <p><em class="bcp14">OPTIONAL</em>. The value of the Domain attribute specifies the domain for which the cookie is valid. If an explicitly specified value does
     636                        not start with a dot, the user agent supplies a leading dot.
     637                     </p>
     638                  </dd>
     639                  <dt>Max-Age=value</dt>
     640                  <dd>
     641                     <p><em class="bcp14">OPTIONAL</em>. The value of the Max-Age attribute is delta-seconds, the lifetime of the cookie in seconds, a decimal non-negative integer.
     642                        To handle cached cookies correctly, a client <em class="bcp14">SHOULD</em> calculate the age of the cookie according to the age calculation rules in the HTTP/1.1 specification <a href="#RFC2616" id="rfc.xref.RFC2616.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. When the age is greater than delta-seconds seconds, the client <em class="bcp14">SHOULD</em> discard the cookie. A value of zero means the cookie <em class="bcp14">SHOULD</em> be discarded immediately.
     643                     </p>
     644                  </dd>
     645                  <dt>Path=value</dt>
     646                  <dd>
     647                     <p><em class="bcp14">OPTIONAL</em>. The value of the Path attribute specifies the subset of URLs on the origin server to which this cookie applies.
     648                     </p>
     649                  </dd>
     650                  <dt>Port[="portlist"]</dt>
     651                  <dd>
     652                     <p><em class="bcp14">OPTIONAL</em>. The Port attribute restricts the port to which a cookie may be returned in a Cookie request header. Note that the syntax
     653                        REQUIREs quotes around the <em class="bcp14">OPTIONAL</em> portlist even if there is only one portnum in portlist.
     654                     </p>
     655                  </dd>
     656                  <dt>Secure</dt>
     657                  <dd>
     658                     <p><em class="bcp14">OPTIONAL</em>. The Secure attribute (with no value) directs the user agent to use only (unspecified) secure means to contact the origin
     659                        server whenever it sends back this cookie, to protect the confidentially and authenticity of the information in the cookie.
     660                     </p>
     661                     <p>The user agent (possibly with user interaction) <em class="bcp14">MAY</em> determine what level of security it considers appropriate for "secure" cookies. The Secure attribute should be considered
     662                        security advice from the server to the user agent, indicating that it is in the session's interest to protect the cookie contents.
     663                        When it sends a "secure" cookie back to a server, the user agent <em class="bcp14">SHOULD</em> use no less than the same level of security as was used when it received the cookie from the server.
     664                     </p>
     665                  </dd>
     666                  <dt>Version=value</dt>
     667                  <dd>
     668                     <p><em class="bcp14">REQUIRED</em>. The value of the Version attribute, a decimal integer, identifies the version of the state management specification to which
     669                        the cookie conforms. For this specification, Version=1 applies.
     670                     </p>
     671                  </dd>
     672               </dl>
     673            </div>
     674            <div>
     675               <h3 id="rfc.section.3.2.3"><a href="#rfc.section.3.2.3">3.2.3</a>&nbsp;Controlling Caching
     676               </h3>
     677               <p id="rfc.section.3.2.3.p.1">An origin server must be cognizant of the effect of possible caching of both the returned resource and the Set-Cookie2 header.
     678                  Caching "public" documents is desirable. For example, if the origin server wants to use a public document such as a "front
     679                  door" page as a sentinel to indicate the beginning of a session for which a Set-Cookie2 response header must be generated,
     680                  the page <em class="bcp14">SHOULD</em> be stored in caches "pre-expired" so that the origin server will see further requests. "Private documents", for example those
     681                  that contain information strictly private to a session, <em class="bcp14">SHOULD</em> NOT be cached in shared caches.
     682               </p>
     683               <p id="rfc.section.3.2.3.p.2">If the cookie is intended for use by a single user, the Set-Cookie2 header <em class="bcp14">SHOULD NOT</em> be cached. A Set-Cookie2 header that is intended to be shared by multiple users <em class="bcp14">MAY</em> be cached.
     684               </p>
     685               <p id="rfc.section.3.2.3.p.3">The origin server <em class="bcp14">SHOULD</em> send the following additional HTTP/1.1 response headers, depending on circumstances:
     686               </p>
     687               <ul>
     688                  <li>To suppress caching of the Set-Cookie2 header:
     689                     <div id="rfc.figure.u.3"></div><pre class="text">
    683690    Cache-control: no-cache="set-cookie2"
    684691</pre> </li>
    685       </ul>
    686       <p id="rfc.section.3.2.3.p.4">and one of the following: </p>
    687       <ul>
    688          <li>To suppress caching of a private document in shared caches:
    689             <div id="rfc.figure.u.4"></div><pre class="text">
     692               </ul>
     693               <p id="rfc.section.3.2.3.p.4">and one of the following: </p>
     694               <ul>
     695                  <li>To suppress caching of a private document in shared caches:
     696                     <div id="rfc.figure.u.4"></div><pre class="text">
    690697    Cache-control: private
    691698</pre> </li>
    692          <li>To allow caching of a document and require that it be validated before returning it to the client:
    693             <div id="rfc.figure.u.5"></div><pre class="text">
     699                  <li>To allow caching of a document and require that it be validated before returning it to the client:
     700                     <div id="rfc.figure.u.5"></div><pre class="text">
    694701    Cache-Control: must-revalidate, max-age=0
    695702</pre> </li>
    696          <li>To allow caching of a document, but to require that proxy caches (not user agent caches) validate it before returning it to
    697             the client:
    698             <div id="rfc.figure.u.6"></div><pre class="text">
     703                  <li>To allow caching of a document, but to require that proxy caches (not user agent caches) validate it before returning it to
     704                     the client:
     705                     <div id="rfc.figure.u.6"></div><pre class="text">
    699706    Cache-Control: proxy-revalidate, max-age=0
    700707</pre> </li>
    701          <li>To allow caching of a document and request that it be validated before returning it to the client (by "pre-expiring" it):
    702             <div id="rfc.figure.u.7"></div><pre class="text">
     708                  <li>To allow caching of a document and request that it be validated before returning it to the client (by "pre-expiring" it):
     709                     <div id="rfc.figure.u.7"></div><pre class="text">
    703710    Cache-control: max-age=0
    704711</pre> Not all caches will revalidate the document in every case.</li>
    705       </ul>
    706       <p id="rfc.section.3.2.3.p.5">HTTP/1.1 servers <em class="bcp14">MUST</em> send Expires: old-date (where old-date is a date long in the past) on responses containing Set-Cookie2 response headers unless
    707          they know for certain (by out of band means) that there are no HTTP/1.0 proxies in the response chain. HTTP/1.1 servers <em class="bcp14">MAY</em> send other Cache-Control directives that permit caching by HTTP/1.1 proxies in addition to the Expires: old-date directive;
    708          the Cache-Control directive will override the Expires: old-date for HTTP/1.1 proxies.
    709       </p>
    710       <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;User Agent Role
    711       </h2>
    712       <h3 id="rfc.section.3.3.1"><a href="#rfc.section.3.3.1">3.3.1</a>&nbsp;Interpreting Set-Cookie2
    713       </h3>
    714       <p id="rfc.section.3.3.1.p.1">The user agent keeps separate track of state information that arrives via Set-Cookie2 response headers from each origin server
    715          (as distinguished by name or IP address and port). The user agent <em class="bcp14">MUST</em> ignore attribute-value pairs whose attribute it does not recognize. The user agent applies these defaults for optional attributes
    716          that are missing:
    717       </p>
    718       <p id="rfc.section.3.3.1.p.2"> </p>
    719       <dl>
    720          <dt>Discard</dt>
    721          <dd>The default behavior is dictated by the presence or absence of a Max-Age attribute.</dd>
    722          <dt>Domain</dt>
    723          <dd>Defaults to the effective request-host. (Note that because there is no dot at the beginning of effective request-host, the
    724             default Domain can only domain-match itself.)
    725          </dd>
    726          <dt>Max-Age</dt>
    727          <dd>The default behavior is to discard the cookie when the user agent exits.</dd>
    728          <dt>Path</dt>
    729          <dd>Defaults to the path of the request URL that generated the Set-Cookie2 response, up to and including the right-most /.</dd>
    730          <dt>Port</dt>
    731          <dd>The default behavior is that a cookie <em class="bcp14">MAY</em> be returned to any request-port.
    732          </dd>
    733          <dt>Secure</dt>
    734          <dd>If absent, the user agent <em class="bcp14">MAY</em> send the cookie over an insecure channel.
    735          </dd>
    736       </dl>
    737       <h3 id="rfc.section.3.3.2"><a href="#rfc.section.3.3.2">3.3.2</a>&nbsp;Rejecting Cookies
    738       </h3>
    739       <p id="rfc.section.3.3.2.p.1">To prevent possible security or privacy violations, a user agent rejects a cookie according to rules below. The goal of the
    740          rules is to try to limit the set of servers for which a cookie is valid, based on the values of the Path, Domain, and Port
    741          attributes and the request-URI, request-host and request-port.
    742       </p>
    743       <p id="rfc.section.3.3.2.p.2">A user agent rejects (<em class="bcp14">SHALL NOT</em> store its information) if the Version attribute is missing. Moreover, a user agent rejects (<em class="bcp14">SHALL NOT</em> store its information) if any of the following is true of the attributes explicitly present in the Set-Cookie2 response header:
    744       </p>
    745       <ul>
    746          <li>The value for the Path attribute is not a prefix of the request-URI.</li>
    747          <li>The value for the Domain attribute contains no embedded dots, and the value is not .local.</li>
    748          <li>The effective host name that derives from the request-host does not domain-match the Domain attribute.</li>
    749          <li>The request-host is a HDN (not IP address) and has the form HD, where D is the value of the Domain attribute, and H is a string
    750             that contains one or more dots.
    751          </li>
    752          <li>The Port attribute has a "port-list", and the request-port was not in the list.</li>
    753       </ul>
    754       <p id="rfc.section.3.3.2.p.3">Examples: </p>
    755       <ul>
    756          <li>A Set-Cookie2 from request-host y.x.foo.com for Domain=.foo.com would be rejected, because H is y.x and contains a dot.</li>
    757          <li>A Set-Cookie2 from request-host x.foo.com for Domain=.foo.com would be accepted.</li>
    758          <li>A Set-Cookie2 with Domain=.com or Domain=.com., will always be rejected, because there is no embedded dot.</li>
    759          <li>A Set-Cookie2 with Domain=ajax.com will be accepted, and the value for Domain will be taken to be .ajax.com, because a dot
    760             gets prepended to the value.
    761          </li>
    762          <li>A Set-Cookie2 with Port="80,8000" will be accepted if the request was made to port 80 or 8000 and will be rejected otherwise.</li>
    763          <li>A Set-Cookie2 from request-host example for Domain=.local will be accepted, because the effective host name for the request-
    764             host is example.local, and example.local domain-matches .local.
    765          </li>
    766       </ul>
    767       <h3 id="rfc.section.3.3.3"><a href="#rfc.section.3.3.3">3.3.3</a>&nbsp;Cookie Management
    768       </h3>
    769       <p id="rfc.section.3.3.3.p.1">If a user agent receives a Set-Cookie2 response header whose NAME is the same as that of a cookie it has previously stored,
    770          the new cookie supersedes the old when: the old and new Domain attribute values compare equal, using a case-insensitive string-compare;
    771          and, the old and new Path attribute values string-compare equal (case-sensitive). However, if the Set-Cookie2 has a value
    772          for Max-Age of zero, the (old and new) cookie is discarded. Otherwise a cookie persists (resources permitting) until whichever
    773          happens first, then gets discarded: its Max-Age lifetime is exceeded; or, if the Discard attribute is set, the user agent
    774          terminates the session.
    775       </p>
    776       <p id="rfc.section.3.3.3.p.2">Because user agents have finite space in which to store cookies, they <em class="bcp14">MAY</em> also discard older cookies to make space for newer ones, using, for example, a least-recently-used algorithm, along with constraints
    777          on the maximum number of cookies that each origin server may set.
    778       </p>
    779       <p id="rfc.section.3.3.3.p.3">If a Set-Cookie2 response header includes a Comment attribute, the user agent <em class="bcp14">SHOULD</em> store that information in a human-readable form with the cookie and <em class="bcp14">SHOULD</em> display the comment text as part of a cookie inspection user interface.
    780       </p>
    781       <p id="rfc.section.3.3.3.p.4">If a Set-Cookie2 response header includes a CommentURL attribute, the user agent <em class="bcp14">SHOULD</em> store that information in a human-readable form with the cookie, or, preferably, <em class="bcp14">SHOULD</em> allow the user to follow the http_URL link as part of a cookie inspection user interface.
    782       </p>
    783       <p id="rfc.section.3.3.3.p.5">The cookie inspection user interface may include a facility whereby a user can decide, at the time the user agent receives
    784          the Set-Cookie2 response header, whether or not to accept the cookie. A potentially confusing situation could arise if the
    785          following sequence occurs:
    786       </p>
    787       <ul>
    788          <li>the user agent receives a cookie that contains a CommentURL attribute;</li>
    789          <li>the user agent's cookie inspection interface is configured so that it presents a dialog to the user before the user agent
    790             accepts the cookie;
    791          </li>
    792          <li>the dialog allows the user to follow the CommentURL link when the user agent receives the cookie; and,</li>
    793          <li>when the user follows the CommentURL link, the origin server (or another server, via other links in the returned content)
    794             returns another cookie.
    795          </li>
    796       </ul>
    797       <p id="rfc.section.3.3.3.p.6">The user agent <em class="bcp14">SHOULD NOT</em> send any cookies in this context. The user agent <em class="bcp14">MAY</em> discard any cookie it receives in this context that the user has not, through some user agent mechanism, deemed acceptable.
    798       </p>
    799       <p id="rfc.section.3.3.3.p.7">User agents <em class="bcp14">SHOULD</em> allow the user to control cookie destruction, but they <em class="bcp14">MUST NOT</em> extend the cookie's lifetime beyond that controlled by the Discard and Max-Age attributes. An infrequently-used cookie may
    800          function as a "preferences file" for network applications, and a user may wish to keep it even if it is the least-recently-used
    801          cookie. One possible implementation would be an interface that allows the permanent storage of a cookie through a checkbox
    802          (or, conversely, its immediate destruction).
    803       </p>
    804       <p id="rfc.section.3.3.3.p.8">Privacy considerations dictate that the user have considerable control over cookie management. The PRIVACY section contains
    805          more information.
    806       </p>
    807       <div id="rfc.iref.c.1"></div>
    808       <div id="rfc.iref.h.2"></div>
    809       <h3 id="rfc.section.3.3.4"><a href="#rfc.section.3.3.4">3.3.4</a>&nbsp;Sending Cookies to the Origin Server
    810       </h3>
    811       <p id="rfc.section.3.3.4.p.1">When it sends a request to an origin server, the user agent includes a Cookie request header if it has stored cookies that
    812          are applicable to the request, based on
    813       </p>
    814       <ul>
    815          <li>the request-host and request-port;</li>
    816          <li>the request-URI;</li>
    817          <li>the cookie's age.</li>
    818       </ul>
    819       <div id="rfc.figure.u.8"></div>
    820       <p>The syntax for the header is:</p><pre class="inline">
     712               </ul>
     713               <p id="rfc.section.3.2.3.p.5">HTTP/1.1 servers <em class="bcp14">MUST</em> send Expires: old-date (where old-date is a date long in the past) on responses containing Set-Cookie2 response headers unless
     714                  they know for certain (by out of band means) that there are no HTTP/1.0 proxies in the response chain. HTTP/1.1 servers <em class="bcp14">MAY</em> send other Cache-Control directives that permit caching by HTTP/1.1 proxies in addition to the Expires: old-date directive;
     715                  the Cache-Control directive will override the Expires: old-date for HTTP/1.1 proxies.
     716               </p>
     717            </div>
     718         </div>
     719         <div>
     720            <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;User Agent Role
     721            </h2>
     722            <div>
     723               <h3 id="rfc.section.3.3.1"><a href="#rfc.section.3.3.1">3.3.1</a>&nbsp;Interpreting Set-Cookie2
     724               </h3>
     725               <p id="rfc.section.3.3.1.p.1">The user agent keeps separate track of state information that arrives via Set-Cookie2 response headers from each origin server
     726                  (as distinguished by name or IP address and port). The user agent <em class="bcp14">MUST</em> ignore attribute-value pairs whose attribute it does not recognize. The user agent applies these defaults for optional attributes
     727                  that are missing:
     728               </p>
     729               <p id="rfc.section.3.3.1.p.2"></p>
     730               <dl>
     731                  <dt>Discard</dt>
     732                  <dd>The default behavior is dictated by the presence or absence of a Max-Age attribute.</dd>
     733                  <dt>Domain</dt>
     734                  <dd>Defaults to the effective request-host. (Note that because there is no dot at the beginning of effective request-host, the
     735                     default Domain can only domain-match itself.)
     736                  </dd>
     737                  <dt>Max-Age</dt>
     738                  <dd>The default behavior is to discard the cookie when the user agent exits.</dd>
     739                  <dt>Path</dt>
     740                  <dd>Defaults to the path of the request URL that generated the Set-Cookie2 response, up to and including the right-most /.</dd>
     741                  <dt>Port</dt>
     742                  <dd>The default behavior is that a cookie <em class="bcp14">MAY</em> be returned to any request-port.
     743                  </dd>
     744                  <dt>Secure</dt>
     745                  <dd>If absent, the user agent <em class="bcp14">MAY</em> send the cookie over an insecure channel.
     746                  </dd>
     747               </dl>
     748            </div>
     749            <div>
     750               <h3 id="rfc.section.3.3.2"><a href="#rfc.section.3.3.2">3.3.2</a>&nbsp;Rejecting Cookies
     751               </h3>
     752               <p id="rfc.section.3.3.2.p.1">To prevent possible security or privacy violations, a user agent rejects a cookie according to rules below. The goal of the
     753                  rules is to try to limit the set of servers for which a cookie is valid, based on the values of the Path, Domain, and Port
     754                  attributes and the request-URI, request-host and request-port.
     755               </p>
     756               <p id="rfc.section.3.3.2.p.2">A user agent rejects (<em class="bcp14">SHALL NOT</em> store its information) if the Version attribute is missing. Moreover, a user agent rejects (<em class="bcp14">SHALL NOT</em> store its information) if any of the following is true of the attributes explicitly present in the Set-Cookie2 response header:
     757               </p>
     758               <ul>
     759                  <li>The value for the Path attribute is not a prefix of the request-URI.</li>
     760                  <li>The value for the Domain attribute contains no embedded dots, and the value is not .local.</li>
     761                  <li>The effective host name that derives from the request-host does not domain-match the Domain attribute.</li>
     762                  <li>The request-host is a HDN (not IP address) and has the form HD, where D is the value of the Domain attribute, and H is a string
     763                     that contains one or more dots.
     764                  </li>
     765                  <li>The Port attribute has a "port-list", and the request-port was not in the list.</li>
     766               </ul>
     767               <p id="rfc.section.3.3.2.p.3">Examples: </p>
     768               <ul>
     769                  <li>A Set-Cookie2 from request-host y.x.foo.com for Domain=.foo.com would be rejected, because H is y.x and contains a dot.</li>
     770                  <li>A Set-Cookie2 from request-host x.foo.com for Domain=.foo.com would be accepted.</li>
     771                  <li>A Set-Cookie2 with Domain=.com or Domain=.com., will always be rejected, because there is no embedded dot.</li>
     772                  <li>A Set-Cookie2 with Domain=ajax.com will be accepted, and the value for Domain will be taken to be .ajax.com, because a dot
     773                     gets prepended to the value.
     774                  </li>
     775                  <li>A Set-Cookie2 with Port="80,8000" will be accepted if the request was made to port 80 or 8000 and will be rejected otherwise.</li>
     776                  <li>A Set-Cookie2 from request-host example for Domain=.local will be accepted, because the effective host name for the request-
     777                     host is example.local, and example.local domain-matches .local.
     778                  </li>
     779               </ul>
     780            </div>
     781            <div>
     782               <h3 id="rfc.section.3.3.3"><a href="#rfc.section.3.3.3">3.3.3</a>&nbsp;Cookie Management
     783               </h3>
     784               <p id="rfc.section.3.3.3.p.1">If a user agent receives a Set-Cookie2 response header whose NAME is the same as that of a cookie it has previously stored,
     785                  the new cookie supersedes the old when: the old and new Domain attribute values compare equal, using a case-insensitive string-compare;
     786                  and, the old and new Path attribute values string-compare equal (case-sensitive). However, if the Set-Cookie2 has a value
     787                  for Max-Age of zero, the (old and new) cookie is discarded. Otherwise a cookie persists (resources permitting) until whichever
     788                  happens first, then gets discarded: its Max-Age lifetime is exceeded; or, if the Discard attribute is set, the user agent
     789                  terminates the session.
     790               </p>
     791               <p id="rfc.section.3.3.3.p.2">Because user agents have finite space in which to store cookies, they <em class="bcp14">MAY</em> also discard older cookies to make space for newer ones, using, for example, a least-recently-used algorithm, along with constraints
     792                  on the maximum number of cookies that each origin server may set.
     793               </p>
     794               <p id="rfc.section.3.3.3.p.3">If a Set-Cookie2 response header includes a Comment attribute, the user agent <em class="bcp14">SHOULD</em> store that information in a human-readable form with the cookie and <em class="bcp14">SHOULD</em> display the comment text as part of a cookie inspection user interface.
     795               </p>
     796               <p id="rfc.section.3.3.3.p.4">If a Set-Cookie2 response header includes a CommentURL attribute, the user agent <em class="bcp14">SHOULD</em> store that information in a human-readable form with the cookie, or, preferably, <em class="bcp14">SHOULD</em> allow the user to follow the http_URL link as part of a cookie inspection user interface.
     797               </p>
     798               <p id="rfc.section.3.3.3.p.5">The cookie inspection user interface may include a facility whereby a user can decide, at the time the user agent receives
     799                  the Set-Cookie2 response header, whether or not to accept the cookie. A potentially confusing situation could arise if the
     800                  following sequence occurs:
     801               </p>
     802               <ul>
     803                  <li>the user agent receives a cookie that contains a CommentURL attribute;</li>
     804                  <li>the user agent's cookie inspection interface is configured so that it presents a dialog to the user before the user agent
     805                     accepts the cookie;
     806                  </li>
     807                  <li>the dialog allows the user to follow the CommentURL link when the user agent receives the cookie; and,</li>
     808                  <li>when the user follows the CommentURL link, the origin server (or another server, via other links in the returned content)
     809                     returns another cookie.
     810                  </li>
     811               </ul>
     812               <p id="rfc.section.3.3.3.p.6">The user agent <em class="bcp14">SHOULD NOT</em> send any cookies in this context. The user agent <em class="bcp14">MAY</em> discard any cookie it receives in this context that the user has not, through some user agent mechanism, deemed acceptable.
     813               </p>
     814               <p id="rfc.section.3.3.3.p.7">User agents <em class="bcp14">SHOULD</em> allow the user to control cookie destruction, but they <em class="bcp14">MUST NOT</em> extend the cookie's lifetime beyond that controlled by the Discard and Max-Age attributes. An infrequently-used cookie may
     815                  function as a "preferences file" for network applications, and a user may wish to keep it even if it is the least-recently-used
     816                  cookie. One possible implementation would be an interface that allows the permanent storage of a cookie through a checkbox
     817                  (or, conversely, its immediate destruction).
     818               </p>
     819               <p id="rfc.section.3.3.3.p.8">Privacy considerations dictate that the user have considerable control over cookie management. The PRIVACY section contains
     820                  more information.
     821               </p>
     822            </div>
     823            <div>
     824               <div id="rfc.iref.c.1"></div>
     825               <div id="rfc.iref.h.2"></div>
     826               <h3 id="rfc.section.3.3.4"><a href="#rfc.section.3.3.4">3.3.4</a>&nbsp;Sending Cookies to the Origin Server
     827               </h3>
     828               <p id="rfc.section.3.3.4.p.1">When it sends a request to an origin server, the user agent includes a Cookie request header if it has stored cookies that
     829                  are applicable to the request, based on
     830               </p>
     831               <ul>
     832                  <li>the request-host and request-port;</li>
     833                  <li>the request-URI;</li>
     834                  <li>the cookie's age.</li>
     835               </ul>
     836               <div id="rfc.figure.u.8"></div>
     837               <p>The syntax for the header is:</p><pre class="inline">
    821838cookie          =  "Cookie:" cookie-version 1*((";" | ",") cookie-value)
    822839cookie-value    =  NAME "=" VALUE [";" path] [";" domain] [";" port]
     
    828845port            =  "$Port" [ "=" &lt;"&gt; value &lt;"&gt; ]
    829846</pre><p id="rfc.section.3.3.4.p.3">The value of the cookie-version attribute <em class="bcp14">MUST</em> be the value from the Version attribute of the corresponding Set-Cookie2 response header. Otherwise the value for cookie-version
    830          is 0. The value for the path attribute <em class="bcp14">MUST</em> be the value from the Path attribute, if one was present, of the corresponding Set-Cookie2 response header. Otherwise the
    831          attribute <em class="bcp14">SHOULD</em> be omitted from the Cookie request header. The value for the domain attribute <em class="bcp14">MUST</em> be the value from the Domain attribute, if one was present, of the corresponding Set-Cookie2 response header. Otherwise the
    832          attribute <em class="bcp14">SHOULD</em> be omitted from the Cookie request header.
    833       </p>
    834       <p id="rfc.section.3.3.4.p.4">The port attribute of the Cookie request header <em class="bcp14">MUST</em> mirror the Port attribute, if one was present, in the corresponding Set-Cookie2 response header. That is, the port attribute <em class="bcp14">MUST</em> be present if the Port attribute was present in the Set-Cookie2 header, and it <em class="bcp14">MUST</em> have the same value, if any. Otherwise, if the Port attribute was absent from the Set-Cookie2 header, the attribute likewise <em class="bcp14">MUST</em> be omitted from the Cookie request header.
    835       </p>
    836       <p id="rfc.section.3.3.4.p.5">Note that there is neither a Comment nor a CommentURL attribute in the Cookie request header corresponding to the ones in
    837          the Set-Cookie2 response header. The user agent does not return the comment information to the origin server.
    838       </p>
    839       <p id="rfc.section.3.3.4.p.6">The user agent applies the following rules to choose applicable cookie-values to send in Cookie request headers from among
    840          all the cookies it has received.
    841       </p>
    842       <dl>
    843          <dt>Domain Selection</dt>
    844          <dd>The origin server's effective host name <em class="bcp14">MUST</em> domain-match the Domain attribute of the cookie.
    845          </dd>
    846          <dt>Port Selection</dt>
    847          <dd>There are three possible behaviors, depending on the Port attribute in the Set-Cookie2 response header:
    848             <ol>
    849                <li>By default (no Port attribute), the cookie <em class="bcp14">MAY</em> be sent to any port.
    850                </li>
    851                <li>If the attribute is present but has no value (e.g., Port), the cookie <em class="bcp14">MUST</em> only be sent to the request-port it was received from.
    852                </li>
    853                <li>If the attribute has a port-list, the cookie <em class="bcp14">MUST</em> only be returned if the new request-port is one of those listed in port-list.
    854                </li>
    855             </ol>
    856          </dd>
    857          <dt>Path Selection</dt>
    858          <dd>The request-URI <em class="bcp14">MUST</em> path-match the Path attribute of the cookie.
    859          </dd>
    860          <dt>Max-Age Selection</dt>
    861          <dd>Cookies that have expired should have been discarded and thus are not forwarded to an origin server.</dd>
    862       </dl>
    863       <p id="rfc.section.3.3.4.p.7">If multiple cookies satisfy the criteria above, they are ordered in the Cookie header such that those with more specific Path
    864          attributes precede those with less specific. Ordering with respect to other attributes (e.g., Domain) is unspecified.
    865       </p>
    866       <p id="rfc.section.3.3.4.p.8">Note: For backward compatibility, the separator in the Cookie header is semi-colon (;) everywhere. A server <em class="bcp14">SHOULD</em> also accept comma (,) as the separator between cookie-values for future compatibility.
    867       </p>
    868       <div id="rfc.iref.c.2"></div>
    869       <div id="rfc.iref.h.3"></div>
    870       <h3 id="rfc.section.3.3.5"><a href="#rfc.section.3.3.5">3.3.5</a>&nbsp;Identifying What Version is Understood:  Cookie2
    871       </h3>
    872       <p id="rfc.section.3.3.5.p.1">The Cookie2 request header facilitates interoperation between clients and servers that understand different versions of the
    873          cookie specification. When the client sends one or more cookies to an origin server, if at least one of those cookies contains
    874          a $Version attribute whose value is different from the version that the client understands, then the client <em class="bcp14">MUST</em> also send a Cookie2 request header, the syntax for which is
    875       </p>
    876       <div id="rfc.figure.u.9"></div><pre class="inline">
     847                  is 0. The value for the path attribute <em class="bcp14">MUST</em> be the value from the Path attribute, if one was present, of the corresponding Set-Cookie2 response header. Otherwise the
     848                  attribute <em class="bcp14">SHOULD</em> be omitted from the Cookie request header. The value for the domain attribute <em class="bcp14">MUST</em> be the value from the Domain attribute, if one was present, of the corresponding Set-Cookie2 response header. Otherwise the
     849                  attribute <em class="bcp14">SHOULD</em> be omitted from the Cookie request header.
     850               </p>
     851               <p id="rfc.section.3.3.4.p.4">The port attribute of the Cookie request header <em class="bcp14">MUST</em> mirror the Port attribute, if one was present, in the corresponding Set-Cookie2 response header. That is, the port attribute <em class="bcp14">MUST</em> be present if the Port attribute was present in the Set-Cookie2 header, and it <em class="bcp14">MUST</em> have the same value, if any. Otherwise, if the Port attribute was absent from the Set-Cookie2 header, the attribute likewise <em class="bcp14">MUST</em> be omitted from the Cookie request header.
     852               </p>
     853               <p id="rfc.section.3.3.4.p.5">Note that there is neither a Comment nor a CommentURL attribute in the Cookie request header corresponding to the ones in
     854                  the Set-Cookie2 response header. The user agent does not return the comment information to the origin server.
     855               </p>
     856               <p id="rfc.section.3.3.4.p.6">The user agent applies the following rules to choose applicable cookie-values to send in Cookie request headers from among
     857                  all the cookies it has received.
     858               </p>
     859               <dl>
     860                  <dt>Domain Selection</dt>
     861                  <dd>The origin server's effective host name <em class="bcp14">MUST</em> domain-match the Domain attribute of the cookie.
     862                  </dd>
     863                  <dt>Port Selection</dt>
     864                  <dd>There are three possible behaviors, depending on the Port attribute in the Set-Cookie2 response header:
     865                     <ol>
     866                        <li>By default (no Port attribute), the cookie <em class="bcp14">MAY</em> be sent to any port.
     867                        </li>
     868                        <li>If the attribute is present but has no value (e.g., Port), the cookie <em class="bcp14">MUST</em> only be sent to the request-port it was received from.
     869                        </li>
     870                        <li>If the attribute has a port-list, the cookie <em class="bcp14">MUST</em> only be returned if the new request-port is one of those listed in port-list.
     871                        </li>
     872                     </ol>
     873                  </dd>
     874                  <dt>Path Selection</dt>
     875                  <dd>The request-URI <em class="bcp14">MUST</em> path-match the Path attribute of the cookie.
     876                  </dd>
     877                  <dt>Max-Age Selection</dt>
     878                  <dd>Cookies that have expired should have been discarded and thus are not forwarded to an origin server.</dd>
     879               </dl>
     880               <p id="rfc.section.3.3.4.p.7">If multiple cookies satisfy the criteria above, they are ordered in the Cookie header such that those with more specific Path
     881                  attributes precede those with less specific. Ordering with respect to other attributes (e.g., Domain) is unspecified.
     882               </p>
     883               <p id="rfc.section.3.3.4.p.8">Note: For backward compatibility, the separator in the Cookie header is semi-colon (;) everywhere. A server <em class="bcp14">SHOULD</em> also accept comma (,) as the separator between cookie-values for future compatibility.
     884               </p>
     885            </div>
     886            <div>
     887               <div id="rfc.iref.c.2"></div>
     888               <div id="rfc.iref.h.3"></div>
     889               <h3 id="rfc.section.3.3.5"><a href="#rfc.section.3.3.5">3.3.5</a>&nbsp;Identifying What Version is Understood:  Cookie2
     890               </h3>
     891               <p id="rfc.section.3.3.5.p.1">The Cookie2 request header facilitates interoperation between clients and servers that understand different versions of the
     892                  cookie specification. When the client sends one or more cookies to an origin server, if at least one of those cookies contains
     893                  a $Version attribute whose value is different from the version that the client understands, then the client <em class="bcp14">MUST</em> also send a Cookie2 request header, the syntax for which is
     894               </p>
     895               <div id="rfc.figure.u.9"></div><pre class="inline">
    877896   cookie2 =       "Cookie2:" cookie-version
    878897</pre><p id="rfc.section.3.3.5.p.3">Here the value for cookie-version is the highest version of cookie specification (currently 1) that the client understands.
    879          The client needs to send at most one such request header per request.
    880       </p>
    881       <h3 id="rfc.section.3.3.6"><a href="#rfc.section.3.3.6">3.3.6</a>&nbsp;Sending Cookies in Unverifiable Transactions
    882       </h3>
    883       <p id="rfc.section.3.3.6.p.1">Users <em class="bcp14">MUST</em> have control over sessions in order to ensure privacy. (See PRIVACY section below.) To simplify implementation and to prevent
    884          an additional layer of complexity where adequate safeguards exist, however, this document distinguishes between transactions
    885          that are verifiable and those that are unverifiable. A transaction is verifiable if the user, or a user-designated agent,
    886          has the option to review the request-URI prior to its use in the transaction. A transaction is unverifiable if the user does
    887          not have that option. Unverifiable transactions typically arise when a user agent automatically requests inlined or embedded
    888          entities or when it resolves redirection (3xx) responses from an origin server. Typically the origin transaction, the transaction
    889          that the user initiates, is verifiable, and that transaction may directly or indirectly induce the user agent to make unverifiable
    890          transactions.
    891       </p>
    892       <p id="rfc.section.3.3.6.p.2">An unverifiable transaction is to a third-party host if its request-host U does not domain-match the reach R of the request-host
    893          O in the origin transaction.
    894       </p>
    895       <p id="rfc.section.3.3.6.p.3">When it makes an unverifiable transaction, a user agent <em class="bcp14">MUST</em> disable all cookie processing (i.e., <em class="bcp14">MUST NOT</em> send cookies, and <em class="bcp14">MUST NOT</em> accept any received cookies) if the transaction is to a third-party host.
    896       </p>
    897       <p id="rfc.section.3.3.6.p.4">This restriction prevents a malicious service author from using unverifiable transactions to induce a user agent to start
    898          or continue a session with a server in a different domain. The starting or continuation of such sessions could be contrary
    899          to the privacy expectations of the user, and could also be a security problem.
    900       </p>
    901       <p id="rfc.section.3.3.6.p.5">User agents <em class="bcp14">MAY</em> offer configurable options that allow the user agent, or any autonomous programs that the user agent executes, to ignore the
    902          above rule, so long as these override options default to "off".
    903       </p>
    904       <p id="rfc.section.3.3.6.p.6">(N.B. Mechanisms may be proposed that will automate overriding the third-party restrictions under controlled conditions.)</p>
    905       <p id="rfc.section.3.3.6.p.7">Many current user agents already provide a review option that would render many links verifiable. For instance, some user
    906          agents display the URL that would be referenced for a particular link when the mouse pointer is placed over that link. The
    907          user can therefore determine whether to visit that site before causing the browser to do so. (Though not implemented on current
    908          user agents, a similar technique could be used for a button used to submit a form -- the user agent could display the action
    909          to be taken if the user were to select that button.) However, even this would not make all links verifiable; for example,
    910          links to automatically loaded images would not normally be subject to "mouse pointer" verification.
    911       </p>
    912       <p id="rfc.section.3.3.6.p.8">Many user agents also provide the option for a user to view the HTML source of a document, or to save the source to an external
    913          file where it can be viewed by another application. While such an option does provide a crude review mechanism, some users
    914          might not consider it acceptable for this purpose.
    915       </p>
    916       <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;How an Origin Server Interprets the Cookie Header
    917       </h2>
    918       <p id="rfc.section.3.4.p.1">A user agent returns much of the information in the Set-Cookie2 header to the origin server when the request-URI path-matches
    919          the Path attribute of the cookie. When it receives a Cookie header, the origin server <em class="bcp14">SHOULD</em> treat cookies with NAMEs whose prefix is $ specially, as an attribute for the cookie.
    920       </p>
    921       <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;Caching Proxy Role
    922       </h2>
    923       <p id="rfc.section.3.5.p.1">One reason for separating state information from both a URL and document content is to facilitate the scaling that caching
    924          permits. To support cookies, a caching proxy <em class="bcp14">MUST</em> obey these rules already in the HTTP specification:
    925       </p>
    926       <ul>
    927          <li>Honor requests from the cache, if possible, based on cache validity rules.</li>
    928          <li>Pass along a Cookie request header in any request that the proxy must make of another server.</li>
    929          <li>Return the response to the client. Include any Set-Cookie2 response header.</li>
    930          <li>Cache the received response subject to the control of the usual headers, such as Expires,
    931             <div id="rfc.figure.u.10"></div><pre class="text">
     898                  The client needs to send at most one such request header per request.
     899               </p>
     900            </div>
     901            <div>
     902               <h3 id="rfc.section.3.3.6"><a href="#rfc.section.3.3.6">3.3.6</a>&nbsp;Sending Cookies in Unverifiable Transactions
     903               </h3>
     904               <p id="rfc.section.3.3.6.p.1">Users <em class="bcp14">MUST</em> have control over sessions in order to ensure privacy. (See PRIVACY section below.) To simplify implementation and to prevent
     905                  an additional layer of complexity where adequate safeguards exist, however, this document distinguishes between transactions
     906                  that are verifiable and those that are unverifiable. A transaction is verifiable if the user, or a user-designated agent,
     907                  has the option to review the request-URI prior to its use in the transaction. A transaction is unverifiable if the user does
     908                  not have that option. Unverifiable transactions typically arise when a user agent automatically requests inlined or embedded
     909                  entities or when it resolves redirection (3xx) responses from an origin server. Typically the origin transaction, the transaction
     910                  that the user initiates, is verifiable, and that transaction may directly or indirectly induce the user agent to make unverifiable
     911                  transactions.
     912               </p>
     913               <p id="rfc.section.3.3.6.p.2">An unverifiable transaction is to a third-party host if its request-host U does not domain-match the reach R of the request-host
     914                  O in the origin transaction.
     915               </p>
     916               <p id="rfc.section.3.3.6.p.3">When it makes an unverifiable transaction, a user agent <em class="bcp14">MUST</em> disable all cookie processing (i.e., <em class="bcp14">MUST NOT</em> send cookies, and <em class="bcp14">MUST NOT</em> accept any received cookies) if the transaction is to a third-party host.
     917               </p>
     918               <p id="rfc.section.3.3.6.p.4">This restriction prevents a malicious service author from using unverifiable transactions to induce a user agent to start
     919                  or continue a session with a server in a different domain. The starting or continuation of such sessions could be contrary
     920                  to the privacy expectations of the user, and could also be a security problem.
     921               </p>
     922               <p id="rfc.section.3.3.6.p.5">User agents <em class="bcp14">MAY</em> offer configurable options that allow the user agent, or any autonomous programs that the user agent executes, to ignore the
     923                  above rule, so long as these override options default to "off".
     924               </p>
     925               <p id="rfc.section.3.3.6.p.6">(N.B. Mechanisms may be proposed that will automate overriding the third-party restrictions under controlled conditions.)</p>
     926               <p id="rfc.section.3.3.6.p.7">Many current user agents already provide a review option that would render many links verifiable. For instance, some user
     927                  agents display the URL that would be referenced for a particular link when the mouse pointer is placed over that link. The
     928                  user can therefore determine whether to visit that site before causing the browser to do so. (Though not implemented on current
     929                  user agents, a similar technique could be used for a button used to submit a form -- the user agent could display the action
     930                  to be taken if the user were to select that button.) However, even this would not make all links verifiable; for example,
     931                  links to automatically loaded images would not normally be subject to "mouse pointer" verification.
     932               </p>
     933               <p id="rfc.section.3.3.6.p.8">Many user agents also provide the option for a user to view the HTML source of a document, or to save the source to an external
     934                  file where it can be viewed by another application. While such an option does provide a crude review mechanism, some users
     935                  might not consider it acceptable for this purpose.
     936               </p>
     937            </div>
     938         </div>
     939         <div>
     940            <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;How an Origin Server Interprets the Cookie Header
     941            </h2>
     942            <p id="rfc.section.3.4.p.1">A user agent returns much of the information in the Set-Cookie2 header to the origin server when the request-URI path-matches
     943               the Path attribute of the cookie. When it receives a Cookie header, the origin server <em class="bcp14">SHOULD</em> treat cookies with NAMEs whose prefix is $ specially, as an attribute for the cookie.
     944            </p>
     945         </div>
     946         <div>
     947            <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;Caching Proxy Role
     948            </h2>
     949            <p id="rfc.section.3.5.p.1">One reason for separating state information from both a URL and document content is to facilitate the scaling that caching
     950               permits. To support cookies, a caching proxy <em class="bcp14">MUST</em> obey these rules already in the HTTP specification:
     951            </p>
     952            <ul>
     953               <li>Honor requests from the cache, if possible, based on cache validity rules.</li>
     954               <li>Pass along a Cookie request header in any request that the proxy must make of another server.</li>
     955               <li>Return the response to the client. Include any Set-Cookie2 response header.</li>
     956               <li>Cache the received response subject to the control of the usual headers, such as Expires,
     957                  <div id="rfc.figure.u.10"></div><pre class="text">
    932958   Cache-control: no-cache
    933959</pre> and <div id="rfc.figure.u.11"></div><pre class="text">
    934960   Cache-control: private
    935961</pre> </li>
    936          <li>Cache the Set-Cookie2 subject to the control of the usual header,
    937             <div id="rfc.figure.u.12"></div><pre class="text">
     962               <li>Cache the Set-Cookie2 subject to the control of the usual header,
     963                  <div id="rfc.figure.u.12"></div><pre class="text">
    938964   Cache-control: no-cache="set-cookie2"
    939965</pre> (The Set-Cookie2 header should usually not be cached.)</li>
    940       </ul>
    941       <p id="rfc.section.3.5.p.2">Proxies <em class="bcp14">MUST NOT</em> introduce Set-Cookie2 (Cookie) headers of their own in proxy responses (requests).
    942       </p>
     966            </ul>
     967            <p id="rfc.section.3.5.p.2">Proxies <em class="bcp14">MUST NOT</em> introduce Set-Cookie2 (Cookie) headers of their own in proxy responses (requests).
     968            </p>
     969         </div>
     970      </div>
    943971      <hr class="noprint">
    944       <h1 id="rfc.section.4" class="np"><a href="#rfc.section.4">4.</a>&nbsp;EXAMPLES
    945       </h1>
    946       <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;Example 1
    947       </h2>
    948       <p id="rfc.section.4.1.p.1">Most detail of request and response headers has been omitted. Assume the user agent has no stored cookies.</p>
    949       <p id="rfc.section.4.1.p.2">1. User Agent -&gt; Server</p>
    950       <div id="rfc.figure.u.13"></div><pre class="text2">
     972      <div>
     973         <h1 id="rfc.section.4" class="np"><a href="#rfc.section.4">4.</a>&nbsp;EXAMPLES
     974         </h1>
     975         <div>
     976            <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;Example 1
     977            </h2>
     978            <p id="rfc.section.4.1.p.1">Most detail of request and response headers has been omitted. Assume the user agent has no stored cookies.</p>
     979            <p id="rfc.section.4.1.p.2">1. User Agent -&gt; Server</p>
     980            <div id="rfc.figure.u.13"></div><pre class="text2">
    951981    POST /acme/login HTTP/1.1
    952982    [form data]
    953983</pre><p id="rfc.section.4.1.p.4">User identifies self via a form.</p>
    954       <p id="rfc.section.4.1.p.5">2. Server -&gt; User Agent</p>
    955       <div id="rfc.figure.u.14"></div><pre class="text">
     984            <p id="rfc.section.4.1.p.5">2. Server -&gt; User Agent</p>
     985            <div id="rfc.figure.u.14"></div><pre class="text">
    956986    HTTP/1.1 200 OK
    957987    Set-Cookie2: Customer="WILE_E_COYOTE"; Version="1"; Path="/acme"
    958988</pre><p id="rfc.section.4.1.p.7">Cookie reflects user's identity.</p>
    959       <p id="rfc.section.4.1.p.8">3. User Agent -&gt; Server</p>
    960       <div id="rfc.figure.u.15"></div><pre class="text2">
     989            <p id="rfc.section.4.1.p.8">3. User Agent -&gt; Server</p>
     990            <div id="rfc.figure.u.15"></div><pre class="text2">
    961991    POST /acme/pickitem HTTP/1.1
    962992    Cookie: $Version="1"; Customer="WILE_E_COYOTE"; $Path="/acme"
    963993    [form data]
    964994</pre><p id="rfc.section.4.1.p.10">User selects an item for "shopping basket".</p>
    965       <p id="rfc.section.4.1.p.11">4. Server -&gt; User Agent</p>
    966       <div id="rfc.figure.u.16"></div><pre class="text">
     995            <p id="rfc.section.4.1.p.11">4. Server -&gt; User Agent</p>
     996            <div id="rfc.figure.u.16"></div><pre class="text">
    967997    HTTP/1.1 200 OK
    968998    Set-Cookie2: Part_Number="Rocket_Launcher_0001"; Version="1";
    969999            Path="/acme"
    9701000</pre><p id="rfc.section.4.1.p.13">Shopping basket contains an item.</p>
    971       <p id="rfc.section.4.1.p.14">5. User Agent -&gt; Server</p>
    972       <div id="rfc.figure.u.17"></div><pre class="text2">
     1001            <p id="rfc.section.4.1.p.14">5. User Agent -&gt; Server</p>
     1002            <div id="rfc.figure.u.17"></div><pre class="text2">
    9731003    POST /acme/shipping HTTP/1.1
    9741004    Cookie: $Version="1";
     
    9771007    [form data]
    9781008</pre><p id="rfc.section.4.1.p.16">User selects shipping method from form.</p>
    979       <p id="rfc.section.4.1.p.17">6. Server -&gt; User Agent</p>
    980       <div id="rfc.figure.u.18"></div><pre class="text">
     1009            <p id="rfc.section.4.1.p.17">6. Server -&gt; User Agent</p>
     1010            <div id="rfc.figure.u.18"></div><pre class="text">
    9811011    HTTP/1.1 200 OK
    9821012    Set-Cookie2: Shipping="FedEx"; Version="1"; Path="/acme"
    9831013</pre><p id="rfc.section.4.1.p.19">New cookie reflects shipping method.</p>
    984       <p id="rfc.section.4.1.p.20">7. User Agent -&gt; Server</p>
    985       <div id="rfc.figure.u.19"></div><pre class="text2">
     1014            <p id="rfc.section.4.1.p.20">7. User Agent -&gt; Server</p>
     1015            <div id="rfc.figure.u.19"></div><pre class="text2">
    9861016    POST /acme/process HTTP/1.1
    9871017    Cookie: $Version="1";
     
    9911021    [form data]
    9921022</pre><p id="rfc.section.4.1.p.22">User chooses to process order.</p>
    993       <p id="rfc.section.4.1.p.23">8. Server -&gt; User Agent</p>
    994       <div id="rfc.figure.u.20"></div><pre class="text">
     1023            <p id="rfc.section.4.1.p.23">8. Server -&gt; User Agent</p>
     1024            <div id="rfc.figure.u.20"></div><pre class="text">
    9951025    HTTP/1.1 200 OK
    9961026</pre><p id="rfc.section.4.1.p.25">Transaction is complete.</p>
    997       <p id="rfc.section.4.1.p.26">The user agent makes a series of requests on the origin server, after each of which it receives a new cookie. All the cookies
    998          have the same Path attribute and (default) domain. Because the request-URIs all path-match /acme, the Path attribute of each
    999          cookie, each request contains all the cookies received so far.
    1000       </p>
    1001       <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;Example 2
    1002       </h2>
    1003       <p id="rfc.section.4.2.p.1">This example illustrates the effect of the Path attribute. All detail of request and response headers has been omitted. Assume
    1004          the user agent has no stored cookies.
    1005       </p>
    1006       <p id="rfc.section.4.2.p.2">Imagine the user agent has received, in response to earlier requests, the response headers</p>
    1007       <div id="rfc.figure.u.21"></div><pre class="text">
     1027            <p id="rfc.section.4.1.p.26">The user agent makes a series of requests on the origin server, after each of which it receives a new cookie. All the cookies
     1028               have the same Path attribute and (default) domain. Because the request-URIs all path-match /acme, the Path attribute of each
     1029               cookie, each request contains all the cookies received so far.
     1030            </p>
     1031         </div>
     1032         <div>
     1033            <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;Example 2
     1034            </h2>
     1035            <p id="rfc.section.4.2.p.1">This example illustrates the effect of the Path attribute. All detail of request and response headers has been omitted. Assume
     1036               the user agent has no stored cookies.
     1037            </p>
     1038            <p id="rfc.section.4.2.p.2">Imagine the user agent has received, in response to earlier requests, the response headers</p>
     1039            <div id="rfc.figure.u.21"></div><pre class="text">
    10081040   Set-Cookie2: Part_Number="Rocket_Launcher_0001"; Version="1";
    10091041           Path="/acme"
    10101042</pre><p id="rfc.section.4.2.p.4">and</p>
    1011       <div id="rfc.figure.u.22"></div><pre class="text">
     1043            <div id="rfc.figure.u.22"></div><pre class="text">
    10121044   Set-Cookie2: Part_Number="Riding_Rocket_0023"; Version="1";
    10131045           Path="/acme/ammo"
    10141046</pre><p id="rfc.section.4.2.p.6">A subsequent request by the user agent to the (same) server for URLs of the form /acme/ammo/... would include the following
    1015          request header:
    1016       </p>
    1017       <div id="rfc.figure.u.23"></div><pre class="text">
     1047               request header:
     1048            </p>
     1049            <div id="rfc.figure.u.23"></div><pre class="text">
    10181050   Cookie: $Version="1";
    10191051           Part_Number="Riding_Rocket_0023"; $Path="/acme/ammo";
    10201052           Part_Number="Rocket_Launcher_0001"; $Path="/acme"
    10211053</pre><p id="rfc.section.4.2.p.8">Note that the NAME=VALUE pair for the cookie with the more specific Path attribute, /acme/ammo, comes before the one with
    1022          the less specific Path attribute, /acme. Further note that the same cookie name appears more than once.
    1023       </p>
    1024       <p id="rfc.section.4.2.p.9">A subsequent request by the user agent to the (same) server for a URL of the form /acme/parts/ would include the following
    1025          request header:
    1026       </p>
    1027       <div id="rfc.figure.u.24"></div><pre class="text">
     1054               the less specific Path attribute, /acme. Further note that the same cookie name appears more than once.
     1055            </p>
     1056            <p id="rfc.section.4.2.p.9">A subsequent request by the user agent to the (same) server for a URL of the form /acme/parts/ would include the following
     1057               request header:
     1058            </p>
     1059            <div id="rfc.figure.u.24"></div><pre class="text">
    10281060   Cookie: $Version="1"; Part_Number="Rocket_Launcher_0001";
    10291061   $Path="/acme"
    10301062</pre><p id="rfc.section.4.2.p.11">Here, the second cookie's Path attribute /acme/ammo is not a prefix of the request URL, /acme/parts/, so the cookie does not
    1031          get forwarded to the server.
    1032       </p>
     1063               get forwarded to the server.
     1064            </p>
     1065         </div>
     1066      </div>
    10331067      <hr class="noprint">
    1034       <h1 id="rfc.section.5" class="np"><a href="#rfc.section.5">5.</a>&nbsp;IMPLEMENTATION CONSIDERATIONS
    1035       </h1>
    1036       <p id="rfc.section.5.p.1">Here we provide guidance on likely or desirable details for an origin server that implements state management.</p>
    1037       <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;Set-Cookie2 Content
    1038       </h2>
    1039       <p id="rfc.section.5.1.p.1">An origin server's content should probably be divided into disjoint application areas, some of which require the use of state
    1040          information. The application areas can be distinguished by their request URLs. The Set-Cookie2 header can incorporate information
    1041          about the application areas by setting the Path attribute for each one.
    1042       </p>
    1043       <p id="rfc.section.5.1.p.2">The session information can obviously be clear or encoded text that describes state. However, if it grows too large, it can
    1044          become unwieldy. Therefore, an implementor might choose for the session information to be a key to a server-side resource.
    1045          Of course, using a database creates some problems that this state management specification was meant to avoid, namely:
    1046       </p>
    1047       <ol>
    1048          <li>keeping real state on the server side;</li>
    1049          <li>how and when to garbage-collect the database entry, in case the user agent terminates the session by, for example, exiting.</li>
    1050       </ol>
    1051       <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;Stateless Pages
    1052       </h2>
    1053       <p id="rfc.section.5.2.p.1">Caching benefits the scalability of WWW. Therefore it is important to reduce the number of documents that have state embedded
    1054          in them inherently. For example, if a shopping-basket-style application always displays a user's current basket contents on
    1055          each page, those pages cannot be cached, because each user's basket's contents would be different. On the other hand, if each
    1056          page contains just a link that allows the user to "Look at My Shopping Basket", the page can be cached.
    1057       </p>
    1058       <h2 id="rfc.section.5.3"><a href="#rfc.section.5.3">5.3</a>&nbsp;Implementation Limits
    1059       </h2>
    1060       <p id="rfc.section.5.3.p.1">Practical user agent implementations have limits on the number and size of cookies that they can store. In general, user agents'
    1061          cookie support should have no fixed limits. They should strive to store as many frequently-used cookies as possible. Furthermore,
    1062          general-use user agents <em class="bcp14">SHOULD</em> provide each of the following minimum capabilities individually, although not necessarily simultaneously:
    1063       </p>
    1064       <ul>
    1065          <li>at least 300 cookies</li>
    1066          <li>at least 4096 bytes per cookie (as measured by the characters that comprise the cookie non-terminal in the syntax description
    1067             of the Set-Cookie2 header, and as received in the Set-Cookie2 header)
    1068          </li>
    1069          <li>at least 20 cookies per unique host or domain name</li>
    1070       </ul>
    1071       <p id="rfc.section.5.3.p.2">User agents created for specific purposes or for limited-capacity devices <em class="bcp14">SHOULD</em> provide at least 20 cookies of 4096 bytes, to ensure that the user can interact with a session-based origin server.
    1072       </p>
    1073       <p id="rfc.section.5.3.p.3">The information in a Set-Cookie2 response header <em class="bcp14">MUST</em> be retained in its entirety. If for some reason there is inadequate space to store the cookie, it <em class="bcp14">MUST</em> be discarded, not truncated.
    1074       </p>
    1075       <p id="rfc.section.5.3.p.4">Applications should use as few and as small cookies as possible, and they should cope gracefully with the loss of a cookie.</p>
    1076       <h3 id="rfc.section.5.3.1"><a href="#rfc.section.5.3.1">5.3.1</a>&nbsp;Denial of Service Attacks
    1077       </h3>
    1078       <p id="rfc.section.5.3.1.p.1">User agents <em class="bcp14">MAY</em> choose to set an upper bound on the number of cookies to be stored from a given host or domain name or on the size of the
    1079          cookie information. Otherwise a malicious server could attempt to flood a user agent with many cookies, or large cookies,
    1080          on successive responses, which would force out cookies the user agent had received from other servers. However, the minima
    1081          specified above <em class="bcp14">SHOULD</em> still be supported.
    1082       </p>
     1068      <div>
     1069         <h1 id="rfc.section.5" class="np"><a href="#rfc.section.5">5.</a>&nbsp;IMPLEMENTATION CONSIDERATIONS
     1070         </h1>
     1071         <p id="rfc.section.5.p.1">Here we provide guidance on likely or desirable details for an origin server that implements state management.</p>
     1072         <div>
     1073            <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;Set-Cookie2 Content
     1074            </h2>
     1075            <p id="rfc.section.5.1.p.1">An origin server's content should probably be divided into disjoint application areas, some of which require the use of state
     1076               information. The application areas can be distinguished by their request URLs. The Set-Cookie2 header can incorporate information
     1077               about the application areas by setting the Path attribute for each one.
     1078            </p>
     1079            <p id="rfc.section.5.1.p.2">The session information can obviously be clear or encoded text that describes state. However, if it grows too large, it can
     1080               become unwieldy. Therefore, an implementor might choose for the session information to be a key to a server-side resource.
     1081               Of course, using a database creates some problems that this state management specification was meant to avoid, namely:
     1082            </p>
     1083            <ol>
     1084               <li>keeping real state on the server side;</li>
     1085               <li>how and when to garbage-collect the database entry, in case the user agent terminates the session by, for example, exiting.</li>
     1086            </ol>
     1087         </div>
     1088         <div>
     1089            <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;Stateless Pages
     1090            </h2>
     1091            <p id="rfc.section.5.2.p.1">Caching benefits the scalability of WWW. Therefore it is important to reduce the number of documents that have state embedded
     1092               in them inherently. For example, if a shopping-basket-style application always displays a user's current basket contents on
     1093               each page, those pages cannot be cached, because each user's basket's contents would be different. On the other hand, if each
     1094               page contains just a link that allows the user to "Look at My Shopping Basket", the page can be cached.
     1095            </p>
     1096         </div>
     1097         <div>
     1098            <h2 id="rfc.section.5.3"><a href="#rfc.section.5.3">5.3</a>&nbsp;Implementation Limits
     1099            </h2>
     1100            <p id="rfc.section.5.3.p.1">Practical user agent implementations have limits on the number and size of cookies that they can store. In general, user agents'
     1101               cookie support should have no fixed limits. They should strive to store as many frequently-used cookies as possible. Furthermore,
     1102               general-use user agents <em class="bcp14">SHOULD</em> provide each of the following minimum capabilities individually, although not necessarily simultaneously:
     1103            </p>
     1104            <ul>
     1105               <li>at least 300 cookies</li>
     1106               <li>at least 4096 bytes per cookie (as measured by the characters that comprise the cookie non-terminal in the syntax description
     1107                  of the Set-Cookie2 header, and as received in the Set-Cookie2 header)
     1108               </li>
     1109               <li>at least 20 cookies per unique host or domain name</li>
     1110            </ul>
     1111            <p id="rfc.section.5.3.p.2">User agents created for specific purposes or for limited-capacity devices <em class="bcp14">SHOULD</em> provide at least 20 cookies of 4096 bytes, to ensure that the user can interact with a session-based origin server.
     1112            </p>
     1113            <p id="rfc.section.5.3.p.3">The information in a Set-Cookie2 response header <em class="bcp14">MUST</em> be retained in its entirety. If for some reason there is inadequate space to store the cookie, it <em class="bcp14">MUST</em> be discarded, not truncated.
     1114            </p>
     1115            <p id="rfc.section.5.3.p.4">Applications should use as few and as small cookies as possible, and they should cope gracefully with the loss of a cookie.</p>
     1116            <div>
     1117               <h3 id="rfc.section.5.3.1"><a href="#rfc.section.5.3.1">5.3.1</a>&nbsp;Denial of Service Attacks
     1118               </h3>
     1119               <p id="rfc.section.5.3.1.p.1">User agents <em class="bcp14">MAY</em> choose to set an upper bound on the number of cookies to be stored from a given host or domain name or on the size of the
     1120                  cookie information. Otherwise a malicious server could attempt to flood a user agent with many cookies, or large cookies,
     1121                  on successive responses, which would force out cookies the user agent had received from other servers. However, the minima
     1122                  specified above <em class="bcp14">SHOULD</em> still be supported.
     1123               </p>
     1124            </div>
     1125         </div>
     1126      </div>
    10831127      <hr class="noprint">
    1084       <h1 id="rfc.section.6" class="np"><a href="#rfc.section.6">6.</a>&nbsp;PRIVACY
    1085       </h1>
    1086       <p id="rfc.section.6.p.1">Informed consent should guide the design of systems that use cookies. A user should be able to find out how a web site plans
    1087          to use information in a cookie and should be able to choose whether or not those policies are acceptable. Both the user agent
    1088          and the origin server must assist informed consent.
    1089       </p>
    1090       <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;User Agent Control
    1091       </h2>
    1092       <p id="rfc.section.6.1.p.1">An origin server could create a Set-Cookie2 header to track the path of a user through the server. Users may object to this
    1093          behavior as an intrusive accumulation of information, even if their identity is not evident. (Identity might become evident,
    1094          for example, if a user subsequently fills out a form that contains identifying information.) This state management specification
    1095          therefore requires that a user agent give the user control over such a possible intrusion, although the interface through
    1096          which the user is given this control is left unspecified. However, the control mechanisms provided <em class="bcp14">SHALL</em> at least allow the user
    1097       </p>
    1098       <ul>
    1099          <li>to completely disable the sending and saving of cookies.</li>
    1100          <li>to determine whether a stateful session is in progress.</li>
    1101          <li>to control the saving of a cookie on the basis of the cookie's Domain attribute.</li>
    1102       </ul>
    1103       <p id="rfc.section.6.1.p.2">Such control could be provided, for example, by mechanisms </p>
    1104       <ul>
    1105          <li>to notify the user when the user agent is about to send a cookie to the origin server, to offer the option not to begin a
    1106             session.
    1107          </li>
    1108          <li>to display a visual indication that a stateful session is in progress.</li>
    1109          <li>to let the user decide which cookies, if any, should be saved when the user concludes a window or user agent session.</li>
    1110          <li>to let the user examine and delete the contents of a cookie at any time.</li>
    1111       </ul>
    1112       <p id="rfc.section.6.1.p.3">A user agent usually begins execution with no remembered state information. It <em class="bcp14">SHOULD</em> be possible to configure a user agent never to send Cookie headers, in which case it can never sustain state with an origin
    1113          server. (The user agent would then behave like one that is unaware of how to handle Set-Cookie2 response headers.)
    1114       </p>
    1115       <p id="rfc.section.6.1.p.4">When the user agent terminates execution, it <em class="bcp14">SHOULD</em> let the user discard all state information. Alternatively, the user agent <em class="bcp14">MAY</em> ask the user whether state information should be retained; the default should be "no". If the user chooses to retain state
    1116          information, it would be restored the next time the user agent runs.
    1117       </p>
    1118       <p id="rfc.section.6.1.p.5">NOTE: User agents should probably be cautious about using files to store cookies long-term. If a user runs more than one instance
    1119          of the user agent, the cookies could be commingled or otherwise corrupted.
    1120       </p>
    1121       <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;Origin Server Role
    1122       </h2>
    1123       <p id="rfc.section.6.2.p.1">An origin server <em class="bcp14">SHOULD</em> promote informed consent by adding CommentURL or Comment information to the cookies it sends. CommentURL is preferred because
    1124          of the opportunity to provide richer information in a multiplicity of languages.
    1125       </p>
    1126       <h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a>&nbsp;Clear Text
    1127       </h2>
    1128       <p id="rfc.section.6.3.p.1">The information in the Set-Cookie2 and Cookie headers is unprotected. As a consequence: </p>
    1129       <ol>
    1130          <li>Any sensitive information that is conveyed in them is exposed to intruders.</li>
    1131          <li>A malicious intermediary could alter the headers as they travel in either direction, with unpredictable results.</li>
    1132       </ol>
    1133       <p id="rfc.section.6.3.p.2">These facts imply that information of a personal and/or financial nature should only be sent over a secure channel. For less
    1134          sensitive information, or when the content of the header is a database key, an origin server should be vigilant to prevent
    1135          a bad Cookie value from causing failures.
    1136       </p>
    1137       <p id="rfc.section.6.3.p.3">A user agent in a shared user environment poses a further risk. Using a cookie inspection interface, User B could examine
    1138          the contents of cookies that were saved when User A used the machine.
    1139       </p>
     1128      <div>
     1129         <h1 id="rfc.section.6" class="np"><a href="#rfc.section.6">6.</a>&nbsp;PRIVACY
     1130         </h1>
     1131         <p id="rfc.section.6.p.1">Informed consent should guide the design of systems that use cookies. A user should be able to find out how a web site plans
     1132            to use information in a cookie and should be able to choose whether or not those policies are acceptable. Both the user agent
     1133            and the origin server must assist informed consent.
     1134         </p>
     1135         <div>
     1136            <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;User Agent Control
     1137            </h2>
     1138            <p id="rfc.section.6.1.p.1">An origin server could create a Set-Cookie2 header to track the path of a user through the server. Users may object to this
     1139               behavior as an intrusive accumulation of information, even if their identity is not evident. (Identity might become evident,
     1140               for example, if a user subsequently fills out a form that contains identifying information.) This state management specification
     1141               therefore requires that a user agent give the user control over such a possible intrusion, although the interface through
     1142               which the user is given this control is left unspecified. However, the control mechanisms provided <em class="bcp14">SHALL</em> at least allow the user
     1143            </p>
     1144            <ul>
     1145               <li>to completely disable the sending and saving of cookies.</li>
     1146               <li>to determine whether a stateful session is in progress.</li>
     1147               <li>to control the saving of a cookie on the basis of the cookie's Domain attribute.</li>
     1148            </ul>
     1149            <p id="rfc.section.6.1.p.2">Such control could be provided, for example, by mechanisms </p>
     1150            <ul>
     1151               <li>to notify the user when the user agent is about to send a cookie to the origin server, to offer the option not to begin a
     1152                  session.
     1153               </li>
     1154               <li>to display a visual indication that a stateful session is in progress.</li>
     1155               <li>to let the user decide which cookies, if any, should be saved when the user concludes a window or user agent session.</li>
     1156               <li>to let the user examine and delete the contents of a cookie at any time.</li>
     1157            </ul>
     1158            <p id="rfc.section.6.1.p.3">A user agent usually begins execution with no remembered state information. It <em class="bcp14">SHOULD</em> be possible to configure a user agent never to send Cookie headers, in which case it can never sustain state with an origin
     1159               server. (The user agent would then behave like one that is unaware of how to handle Set-Cookie2 response headers.)
     1160            </p>
     1161            <p id="rfc.section.6.1.p.4">When the user agent terminates execution, it <em class="bcp14">SHOULD</em> let the user discard all state information. Alternatively, the user agent <em class="bcp14">MAY</em> ask the user whether state information should be retained; the default should be "no". If the user chooses to retain state
     1162               information, it would be restored the next time the user agent runs.
     1163            </p>
     1164            <p id="rfc.section.6.1.p.5">NOTE: User agents should probably be cautious about using files to store cookies long-term. If a user runs more than one instance
     1165               of the user agent, the cookies could be commingled or otherwise corrupted.
     1166            </p>
     1167         </div>
     1168         <div>
     1169            <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;Origin Server Role
     1170            </h2>
     1171            <p id="rfc.section.6.2.p.1">An origin server <em class="bcp14">SHOULD</em> promote informed consent by adding CommentURL or Comment information to the cookies it sends. CommentURL is preferred because
     1172               of the opportunity to provide richer information in a multiplicity of languages.
     1173            </p>
     1174         </div>
     1175         <div>
     1176            <h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a>&nbsp;Clear Text
     1177            </h2>
     1178            <p id="rfc.section.6.3.p.1">The information in the Set-Cookie2 and Cookie headers is unprotected. As a consequence: </p>
     1179            <ol>
     1180               <li>Any sensitive information that is conveyed in them is exposed to intruders.</li>
     1181               <li>A malicious intermediary could alter the headers as they travel in either direction, with unpredictable results.</li>
     1182            </ol>
     1183            <p id="rfc.section.6.3.p.2">These facts imply that information of a personal and/or financial nature should only be sent over a secure channel. For less
     1184               sensitive information, or when the content of the header is a database key, an origin server should be vigilant to prevent
     1185               a bad Cookie value from causing failures.
     1186            </p>
     1187            <p id="rfc.section.6.3.p.3">A user agent in a shared user environment poses a further risk. Using a cookie inspection interface, User B could examine
     1188               the contents of cookies that were saved when User A used the machine.
     1189            </p>
     1190         </div>
     1191      </div>
    11401192      <hr class="noprint">
    1141       <h1 id="rfc.section.7" class="np"><a href="#rfc.section.7">7.</a>&nbsp;SECURITY CONSIDERATIONS
    1142       </h1>
    1143       <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;Protocol Design
    1144       </h2>
    1145       <p id="rfc.section.7.1.p.1">The restrictions on the value of the Domain attribute, and the rules concerning unverifiable transactions, are meant to reduce
    1146          the ways that cookies can "leak" to the "wrong" site. The intent is to restrict cookies to one host, or a closely related
    1147          set of hosts. Therefore a request-host is limited as to what values it can set for Domain. We consider it acceptable for hosts
    1148          host1.foo.com and host2.foo.com to share cookies, but not a.com and b.com.
    1149       </p>
    1150       <p id="rfc.section.7.1.p.2">Similarly, a server can set a Path only for cookies that are related to the request-URI.</p>
    1151       <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;Cookie Spoofing
    1152       </h2>
    1153       <p id="rfc.section.7.2.p.1">Proper application design can avoid spoofing attacks from related domains. Consider: </p>
    1154       <ol>
    1155          <li>User agent makes request to victim.cracker.edu, gets back cookie session_id="1234" and sets the default domain victim.cracker.edu.</li>
    1156          <li>User agent makes request to spoof.cracker.edu, gets back cookie session-id="1111", with Domain=".cracker.edu".</li>
    1157          <li>User agent makes request to victim.cracker.edu again, and passes
    1158             <div id="rfc.figure.u.25"></div><pre class="text">
     1193      <div>
     1194         <h1 id="rfc.section.7" class="np"><a href="#rfc.section.7">7.</a>&nbsp;SECURITY CONSIDERATIONS
     1195         </h1>
     1196         <div>
     1197            <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;Protocol Design
     1198            </h2>
     1199            <p id="rfc.section.7.1.p.1">The restrictions on the value of the Domain attribute, and the rules concerning unverifiable transactions, are meant to reduce
     1200               the ways that cookies can "leak" to the "wrong" site. The intent is to restrict cookies to one host, or a closely related
     1201               set of hosts. Therefore a request-host is limited as to what values it can set for Domain. We consider it acceptable for hosts
     1202               host1.foo.com and host2.foo.com to share cookies, but not a.com and b.com.
     1203            </p>
     1204            <p id="rfc.section.7.1.p.2">Similarly, a server can set a Path only for cookies that are related to the request-URI.</p>
     1205         </div>
     1206         <div>
     1207            <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;Cookie Spoofing
     1208            </h2>
     1209            <p id="rfc.section.7.2.p.1">Proper application design can avoid spoofing attacks from related domains. Consider: </p>
     1210            <ol>
     1211               <li>User agent makes request to victim.cracker.edu, gets back cookie session_id="1234" and sets the default domain victim.cracker.edu.</li>
     1212               <li>User agent makes request to spoof.cracker.edu, gets back cookie session-id="1111", with Domain=".cracker.edu".</li>
     1213               <li>User agent makes request to victim.cracker.edu again, and passes
     1214                  <div id="rfc.figure.u.25"></div><pre class="text">
    11591215     Cookie: $Version="1"; session_id="1234",
    11601216             $Version="1"; session_id="1111"; $Domain=".cracker.edu"
    11611217</pre> The server at victim.cracker.edu should detect that the second cookie was not one it originated by noticing that the Domain
    1162             attribute is not for itself and ignore it.</li>
    1163       </ol>
    1164       <h2 id="rfc.section.7.3"><a href="#rfc.section.7.3">7.3</a>&nbsp;Unexpected Cookie Sharing
    1165       </h2>
    1166       <p id="rfc.section.7.3.p.1">A user agent <em class="bcp14">SHOULD</em> make every attempt to prevent the sharing of session information between hosts that are in different domains. Embedded or
    1167          inlined objects may cause particularly severe privacy problems if they can be used to share cookies between disparate hosts.
    1168          For example, a malicious server could embed cookie information for host a.com in a URI for a CGI on host b.com. User agent
    1169          implementors are strongly encouraged to prevent this sort of exchange whenever possible.
    1170       </p>
    1171       <h2 id="rfc.section.7.4"><a href="#rfc.section.7.4">7.4</a>&nbsp;Cookies For Account Information
    1172       </h2>
    1173       <p id="rfc.section.7.4.p.1">While it is common practice to use them this way, cookies are not designed or intended to be used to hold authentication information,
    1174          such as account names and passwords. Unless such cookies are exchanged over an encrypted path, the account information they
    1175          contain is highly vulnerable to perusal and theft.
    1176       </p>
     1218                  attribute is not for itself and ignore it.</li>
     1219            </ol>
     1220         </div>
     1221         <div>
     1222            <h2 id="rfc.section.7.3"><a href="#rfc.section.7.3">7.3</a>&nbsp;Unexpected Cookie Sharing
     1223            </h2>
     1224            <p id="rfc.section.7.3.p.1">A user agent <em class="bcp14">SHOULD</em> make every attempt to prevent the sharing of session information between hosts that are in different domains. Embedded or
     1225               inlined objects may cause particularly severe privacy problems if they can be used to share cookies between disparate hosts.
     1226               For example, a malicious server could embed cookie information for host a.com in a URI for a CGI on host b.com. User agent
     1227               implementors are strongly encouraged to prevent this sort of exchange whenever possible.
     1228            </p>
     1229         </div>
     1230         <div>
     1231            <h2 id="rfc.section.7.4"><a href="#rfc.section.7.4">7.4</a>&nbsp;Cookies For Account Information
     1232            </h2>
     1233            <p id="rfc.section.7.4.p.1">While it is common practice to use them this way, cookies are not designed or intended to be used to hold authentication information,
     1234               such as account names and passwords. Unless such cookies are exchanged over an encrypted path, the account information they
     1235               contain is highly vulnerable to perusal and theft.
     1236            </p>
     1237         </div>
     1238      </div>
    11771239      <hr class="noprint">
    1178       <h1 id="rfc.section.8" class="np"><a href="#rfc.section.8">8.</a>&nbsp;OTHER, SIMILAR, PROPOSALS
    1179       </h1>
    1180       <p id="rfc.section.8.p.1">Apart from RFC 2109, three other proposals have been made to accomplish similar goals. This specification began as an amalgam
    1181          of Kristol's State-Info proposal <a href="#DMK95" id="rfc.xref.DMK95.1"><cite title="Proposed HTTP State-Info Mechanism">[DMK95]</cite></a> and Netscape's Cookie proposal <a href="#Netscape" id="rfc.xref.Netscape.2"><cite title="Persistent Client State -- HTTP Cookies">[Netscape]</cite></a>.
    1182       </p>
    1183       <p id="rfc.section.8.p.2">Brian Behlendorf proposed a Session-ID header that would be user-agent-initiated and could be used by an origin server to
    1184          track "clicktrails". It would not carry any origin-server-defined state, however. Phillip Hallam-Baker has proposed another
    1185          client-defined session ID mechanism for similar purposes.
    1186       </p>
    1187       <p id="rfc.section.8.p.3">While both session IDs and cookies can provide a way to sustain stateful sessions, their intended purpose is different, and,
    1188          consequently, the privacy requirements for them are different. A user initiates session IDs to allow servers to track progress
    1189          through them, or to distinguish multiple users on a shared machine. Cookies are server-initiated, so the cookie mechanism
    1190          described here gives users control over something that would otherwise take place without the users' awareness. Furthermore,
    1191          cookies convey rich, server-selected information, whereas session IDs comprise user-selected, simple information.
    1192       </p>
     1240      <div>
     1241         <h1 id="rfc.section.8" class="np"><a href="#rfc.section.8">8.</a>&nbsp;OTHER, SIMILAR, PROPOSALS
     1242         </h1>
     1243         <p id="rfc.section.8.p.1">Apart from RFC 2109, three other proposals have been made to accomplish similar goals. This specification began as an amalgam
     1244            of Kristol's State-Info proposal <a href="#DMK95" id="rfc.xref.DMK95.1"><cite title="Proposed HTTP State-Info Mechanism">[DMK95]</cite></a> and Netscape's Cookie proposal <a href="#Netscape" id="rfc.xref.Netscape.2"><cite title="Persistent Client State -- HTTP Cookies">[Netscape]</cite></a>.
     1245         </p>
     1246         <p id="rfc.section.8.p.2">Brian Behlendorf proposed a Session-ID header that would be user-agent-initiated and could be used by an origin server to
     1247            track "clicktrails". It would not carry any origin-server-defined state, however. Phillip Hallam-Baker has proposed another
     1248            client-defined session ID mechanism for similar purposes.
     1249         </p>
     1250         <p id="rfc.section.8.p.3">While both session IDs and cookies can provide a way to sustain stateful sessions, their intended purpose is different, and,
     1251            consequently, the privacy requirements for them are different. A user initiates session IDs to allow servers to track progress
     1252            through them, or to distinguish multiple users on a shared machine. Cookies are server-initiated, so the cookie mechanism
     1253            described here gives users control over something that would otherwise take place without the users' awareness. Furthermore,
     1254            cookies convey rich, server-selected information, whereas session IDs comprise user-selected, simple information.
     1255         </p>
     1256      </div>
    11931257      <hr class="noprint">
    1194       <h1 id="rfc.section.9" class="np"><a href="#rfc.section.9">9.</a>&nbsp;HISTORICAL
    1195       </h1>
    1196       <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;Compatibility with Existing Implementations
    1197       </h2>
    1198       <p id="rfc.section.9.1.p.1">Existing cookie implementations, based on the Netscape specification, use the Set-Cookie (not Set-Cookie2) header. User agents
    1199          that receive in the same response both a Set-Cookie and Set-Cookie2 response header for the same cookie <em class="bcp14">MUST</em> discard the Set-Cookie information and use only the Set-Cookie2 information. Furthermore, a user agent <em class="bcp14">MUST</em> assume, if it received a Set-Cookie2 response header, that the sending server complies with this document and will understand
    1200          Cookie request headers that also follow this specification.
    1201       </p>
    1202       <p id="rfc.section.9.1.p.2">New cookies <em class="bcp14">MUST</em> replace both equivalent old- and new-style cookies. That is, if a user agent that follows both this specification and Netscape's
    1203          original specification receives a Set-Cookie2 response header, and the NAME and the Domain and Path attributes match (per
    1204          the Cookie Management section) a Netscape-style cookie, the Netscape-style cookie <em class="bcp14">MUST</em> be discarded, and the user agent <em class="bcp14">MUST</em> retain only the cookie adhering to this specification.
    1205       </p>
    1206       <p id="rfc.section.9.1.p.3">Older user agents that do not understand this specification, but that do understand Netscape's original specification, will
    1207          not recognize the Set-Cookie2 response header and will receive and send cookies according to the older specification.
    1208       </p>
    1209       <p id="rfc.section.9.1.p.4">A user agent that supports both this specification and Netscape-style cookies <em class="bcp14">SHOULD</em> send a Cookie request header that follows the older Netscape specification if it received the cookie in a Set-Cookie response
    1210          header and not in a Set-Cookie2 response header. However, it <em class="bcp14">SHOULD</em> send the following request header as well:
    1211       </p>
    1212       <div id="rfc.figure.u.26"></div><pre class="text">
     1258      <div>
     1259         <h1 id="rfc.section.9" class="np"><a href="#rfc.section.9">9.</a>&nbsp;HISTORICAL
     1260         </h1>
     1261         <div>
     1262            <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;Compatibility with Existing Implementations
     1263            </h2>
     1264            <p id="rfc.section.9.1.p.1">Existing cookie implementations, based on the Netscape specification, use the Set-Cookie (not Set-Cookie2) header. User agents
     1265               that receive in the same response both a Set-Cookie and Set-Cookie2 response header for the same cookie <em class="bcp14">MUST</em> discard the Set-Cookie information and use only the Set-Cookie2 information. Furthermore, a user agent <em class="bcp14">MUST</em> assume, if it received a Set-Cookie2 response header, that the sending server complies with this document and will understand
     1266               Cookie request headers that also follow this specification.
     1267            </p>
     1268            <p id="rfc.section.9.1.p.2">New cookies <em class="bcp14">MUST</em> replace both equivalent old- and new-style cookies. That is, if a user agent that follows both this specification and Netscape's
     1269               original specification receives a Set-Cookie2 response header, and the NAME and the Domain and Path attributes match (per
     1270               the Cookie Management section) a Netscape-style cookie, the Netscape-style cookie <em class="bcp14">MUST</em> be discarded, and the user agent <em class="bcp14">MUST</em> retain only the cookie adhering to this specification.
     1271            </p>
     1272            <p id="rfc.section.9.1.p.3">Older user agents that do not understand this specification, but that do understand Netscape's original specification, will
     1273               not recognize the Set-Cookie2 response header and will receive and send cookies according to the older specification.
     1274            </p>
     1275            <p id="rfc.section.9.1.p.4">A user agent that supports both this specification and Netscape-style cookies <em class="bcp14">SHOULD</em> send a Cookie request header that follows the older Netscape specification if it received the cookie in a Set-Cookie response
     1276               header and not in a Set-Cookie2 response header. However, it <em class="bcp14">SHOULD</em> send the following request header as well:
     1277            </p>
     1278            <div id="rfc.figure.u.26"></div><pre class="text">
    12131279   Cookie2: $Version="1"
    12141280</pre><p id="rfc.section.9.1.p.6">The Cookie2 header advises the server that the user agent understands new-style cookies. If the server understands new-style
    1215          cookies, as well, it <em class="bcp14">SHOULD</em> continue the stateful session by sending a Set-Cookie2 response header, rather than Set-Cookie. A server that does not understand
    1216          new-style cookies will simply ignore the Cookie2 request header.
    1217       </p>
    1218       <h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;Caching and HTTP/1.0
    1219       </h2>
    1220       <p id="rfc.section.9.2.p.1">Some caches, such as those conforming to HTTP/1.0, will inevitably cache the Set-Cookie2 and Set-Cookie headers, because there
    1221          was no mechanism to suppress caching of headers prior to HTTP/1.1. This caching can lead to security problems. Documents transmitted
    1222          by an origin server along with Set-Cookie2 and Set-Cookie headers usually either will be uncachable, or will be "pre-expired".
    1223          As long as caches obey instructions not to cache documents (following Expires: &lt;a date in the past&gt; or Pragma: no-cache (HTTP/1.0),
    1224          or Cache-control: no-cache (HTTP/1.1)) uncachable documents present no problem. However, pre-expired documents may be stored
    1225          in caches. They require validation (a conditional GET) on each new request, but some cache operators loosen the rules for
    1226          their caches, and sometimes serve expired documents without first validating them. This combination of factors can lead to
    1227          cookies meant for one user later being sent to another user. The Set-Cookie2 and Set-Cookie headers are stored in the cache,
    1228          and, although the document is stale (expired), the cache returns the document in response to later requests, including cached
    1229          headers.
    1230       </p>
     1281               cookies, as well, it <em class="bcp14">SHOULD</em> continue the stateful session by sending a Set-Cookie2 response header, rather than Set-Cookie. A server that does not understand
     1282               new-style cookies will simply ignore the Cookie2 request header.
     1283            </p>
     1284         </div>
     1285         <div>
     1286            <h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;Caching and HTTP/1.0
     1287            </h2>
     1288            <p id="rfc.section.9.2.p.1">Some caches, such as those conforming to HTTP/1.0, will inevitably cache the Set-Cookie2 and Set-Cookie headers, because there
     1289               was no mechanism to suppress caching of headers prior to HTTP/1.1. This caching can lead to security problems. Documents transmitted
     1290               by an origin server along with Set-Cookie2 and Set-Cookie headers usually either will be uncachable, or will be "pre-expired".
     1291               As long as caches obey instructions not to cache documents (following Expires: &lt;a date in the past&gt; or Pragma: no-cache (HTTP/1.0),
     1292               or Cache-control: no-cache (HTTP/1.1)) uncachable documents present no problem. However, pre-expired documents may be stored
     1293               in caches. They require validation (a conditional GET) on each new request, but some cache operators loosen the rules for
     1294               their caches, and sometimes serve expired documents without first validating them. This combination of factors can lead to
     1295               cookies meant for one user later being sent to another user. The Set-Cookie2 and Set-Cookie headers are stored in the cache,
     1296               and, although the document is stale (expired), the cache returns the document in response to later requests, including cached
     1297               headers.
     1298            </p>
     1299         </div>
     1300      </div>
    12311301      <hr class="noprint">
    1232       <h1 id="rfc.section.10" class="np"><a href="#rfc.section.10">10.</a>&nbsp;ACKNOWLEDGEMENTS
    1233       </h1>
    1234       <p id="rfc.section.10.p.1">This document really represents the collective efforts of the HTTP Working Group of the IETF and, particularly, the following
    1235          people, in addition to the authors: Roy Fielding, Yaron Goland, Marc Hedlund, Ted Hardie, Koen Holtman, Shel Kaphan, Rohit
    1236          Khare, Foteos Macrides, David W. Morris.
    1237       </p>
     1302      <div>
     1303         <h1 id="rfc.section.10" class="np"><a href="#rfc.section.10">10.</a>&nbsp;ACKNOWLEDGEMENTS
     1304         </h1>
     1305         <p id="rfc.section.10.p.1">This document really represents the collective efforts of the HTTP Working Group of the IETF and, particularly, the following
     1306            people, in addition to the authors: Roy Fielding, Yaron Goland, Marc Hedlund, Ted Hardie, Koen Holtman, Shel Kaphan, Rohit
     1307            Khare, Foteos Macrides, David W. Morris.
     1308         </p>
     1309      </div>
    12381310      <h1 class="np" id="rfc.references"><a href="#rfc.section.11" id="rfc.section.11">11.</a> References
    12391311      </h1>
    1240       <table> 
     1312      <table>
    12411313         <tr>
    12421314            <td class="reference"><b id="DMK95">[DMK95]</b></td>
    12431315            <td class="top">Kristol, D., “<a href="http://portal.research.bell-labs.com/~dmk/state-info.html">Proposed HTTP State-Info Mechanism</a>”, September&nbsp;1995, &lt;<a href="http://portal.research.bell-labs.com/~dmk/state-info.html">http://portal.research.bell-labs.com/~dmk/state-info.html</a>&gt;.<br>available at &lt;http://portal.research.bell-labs.com/~dmk/state-info.html&gt;
    12441316            </td>
    1245          </tr> 
     1317         </tr>
    12461318         <tr>
    12471319            <td class="reference"><b id="Netscape">[Netscape]</b></td>
    12481320            <td class="top">“<a href="http://www.netscape.com/newsref/std/cookie_spec.html">Persistent Client State -- HTTP Cookies</a>”, &lt;<a href="http://www.netscape.com/newsref/std/cookie_spec.html">http://www.netscape.com/newsref/std/cookie_spec.html</a>&gt;.<br>available at &lt;http://www.netscape.com/newsref/std/cookie_spec.html&gt;
    12491321            </td>
    1250          </tr> 
     1322         </tr>
    12511323         <tr>
    12521324            <td class="reference"><b id="RFC2109">[RFC2109]</b></td>
    12531325            <td class="top"><a href="mailto:dmk@bell-labs.com" title="Bell Laboratories, Lucent Technologies">Kristol, D.</a> and <a href="mailto:montulli@netscape.com" title="Netscape Communications Corp.">L. Montulli</a>, “<a href="http://tools.ietf.org/html/rfc2109">HTTP State Management Mechanism</a>”, RFC&nbsp;2109, February&nbsp;1997.
    12541326            </td>
    1255          </tr> 
     1327         </tr>
    12561328         <tr>
    12571329            <td class="reference"><b id="RFC2119">[RFC2119]</b></td>
    12581330            <td class="top"><a href="mailto:sob@harvard.edu" title="Harvard University">Bradner, S.</a>, “<a href="http://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>”, BCP&nbsp;14, RFC&nbsp;2119, March&nbsp;1997.
    12591331            </td>
    1260          </tr> 
     1332         </tr>
    12611333         <tr>
    12621334            <td class="reference"><b id="RFC2279">[RFC2279]</b></td>
    12631335            <td class="top"><a href="mailto:fyergeau@alis.com" title="Alis Technologies">Yergeau, F.</a>, “<a href="http://tools.ietf.org/html/rfc2279">UTF-8, a transformation format of ISO 10646</a>”, RFC&nbsp;2279, January&nbsp;1998.
    12641336            </td>
    1265          </tr> 
     1337         </tr>
    12661338         <tr>
    12671339            <td class="reference"><b id="RFC2396">[RFC2396]</b></td>
    12681340            <td class="top"><a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:fielding@ics.uci.edu" title="Department of Information and Computer Science">Fielding, R.</a>, and <a href="mailto:masinter@parc.xerox.com" title="Xerox PARC">L. Masinter</a>, “<a href="http://tools.ietf.org/html/rfc2396">Uniform Resource Identifiers (URI): Generic Syntax</a>”, RFC&nbsp;2396, August&nbsp;1998.
    12691341            </td>
    1270          </tr> 
     1342         </tr>
    12711343         <tr>
    12721344            <td class="reference"><b id="RFC2616">[RFC2616]</b></td>
    12731345            <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="W3C">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Compaq Computer Corporation">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Frystyk, H.</a>, <a href="mailto:masinter@parc.xerox.com" title="Xerox Corporation">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="W3C">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/rfc2616">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC&nbsp;2616, June&nbsp;1999.
    12741346            </td>
    1275          </tr> 
     1347         </tr>
    12761348      </table>
    12771349      <hr class="noprint">
    12781350      <div class="avoidbreak">
    12791351         <h1 id="rfc.authors" class="np"><a href="#rfc.authors">Authors' Addresses</a></h1>
    1280          <address class="vcard"><span class="vcardline"><span class="fn">David M. Kristol</span><span class="n hidden"><span class="family-name">Kristol</span><span class="given-name">David M.</span></span></span><span class="org vcardline">Bell Laboratories, Lucent Technologies</span><span class="adr"><span class="street-address vcardline">600 Mountain Ave. Room 2A-333</span><span class="vcardline"><span class="locality">Murray Hill</span>, <span class="region">NJ</span>&nbsp;<span class="postal-code">07974</span></span></span><span class="vcardline tel">Phone: <a href="tel:(908)582-2250"><span class="value">(908) 582-2250</span></a></span><span class="vcardline tel"><span class="type">Fax</span>: <a href="fax:(908)582-1239"><span class="value">(908) 582-1239</span></a></span><span class="vcardline">EMail: <a href="mailto:dmk@bell-labs.com"><span class="email">dmk@bell-labs.com</span></a></span></address>
    1281          <address class="vcard"><span class="vcardline"><span class="fn">Lou Montulli</span><span class="n hidden"><span class="family-name">Montulli</span><span class="given-name">Lou</span></span></span><span class="org vcardline">Epinions.com, Inc.</span><span class="adr"><span class="street-address vcardline">2037 Landings Dr.</span><span class="vcardline"><span class="locality">Mountain View</span>, <span class="region">CA</span>&nbsp;<span class="postal-code">94301</span></span></span><span class="vcardline">EMail: <a href="mailto:lou@montulli.org"><span class="email">lou@montulli.org</span></a></span></address>
     1352         <p><b>David M. Kristol</b><br>Bell Laboratories, Lucent Technologies<br>600 Mountain Ave. Room 2A-333<br>Murray Hill, NJ&nbsp;07974<br>Phone: <a href="tel:(908)582-2250">(908) 582-2250</a><br>Fax: <a href="fax:(908)582-1239">(908) 582-1239</a><br>EMail: <a href="mailto:dmk@bell-labs.com">dmk@bell-labs.com</a></p>
     1353         <p><b>Lou Montulli</b><br>Epinions.com, Inc.<br>2037 Landings Dr.<br>Mountain View, CA&nbsp;94301<br>EMail: <a href="mailto:lou@montulli.org">lou@montulli.org</a></p>
    12821354      </div>
    12831355      <hr class="noprint">
     
    13241396         </ul>
    13251397      </div>
    1326       <h1><a id="rfc.copyright" href="#rfc.copyright">Full Copyright Statement</a></h1>
    1327       <p>Copyright © The Internet Society (2000). All Rights Reserved.</p>
    1328       <p>This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise
    1329          explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without
    1330          restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative
    1331          works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references
    1332          to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards
    1333          in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to
    1334          translate it into languages other than English.
    1335       </p>
    1336       <p>The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.</p>
    1337       <p>This document and the information contained herein is provided on an “AS IS” basis and THE INTERNET SOCIETY AND THE INTERNET
    1338          ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE
    1339          OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
    1340          PURPOSE.
    1341       </p>
     1398      <div id="rfc.copyright">
     1399         <h1><a href="#rfc.copyright">Full Copyright Statement</a></h1>
     1400         <p>Copyright © The Internet Society (2000). All Rights Reserved.</p>
     1401         <p>This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise
     1402            explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without
     1403            restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative
     1404            works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references
     1405            to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards
     1406            in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to
     1407            translate it into languages other than English.
     1408         </p>
     1409         <p>The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.</p>
     1410         <p>This document and the information contained herein is provided on an “AS IS” basis and THE INTERNET SOCIETY AND THE INTERNET
     1411            ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE
     1412            OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
     1413            PURPOSE.
     1414         </p>
     1415      </div>
    13421416      <hr class="noprint">
    1343       <h1 class="np"><a id="rfc.ipr" href="#rfc.ipr">Intellectual Property</a></h1>
    1344       <p>The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed
    1345          to pertain to the implementation or use of the technology described in this document or the extent to which any license under
    1346          such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights.
    1347          Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be
    1348          found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available,
    1349          or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors
    1350          or users of this specification can be obtained from the IETF Secretariat.
    1351       </p>
    1352       <p>The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary
    1353          rights which may cover technology that may be required to practice this standard. Please address the information to the IETF
    1354          Executive Director.
    1355       </p>
    1356       <h1>Acknowledgment</h1>
    1357       <p>Funding for the RFC Editor function is currently provided by the Internet Society.</p>
     1417      <div id="rfc.ipr">
     1418         <h1 class="np"><a href="#rfc.ipr">Intellectual Property</a></h1>
     1419         <p>The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed
     1420            to pertain to the implementation or use of the technology described in this document or the extent to which any license under
     1421            such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights.
     1422            Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be
     1423            found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available,
     1424            or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors
     1425            or users of this specification can be obtained from the IETF Secretariat.
     1426         </p>
     1427         <p>The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary
     1428            rights which may cover technology that may be required to practice this standard. Please address the information to the IETF
     1429            Executive Director.
     1430         </p>
     1431      </div>
     1432      <div>
     1433         <h1>Acknowledgment</h1>
     1434         <p>Funding for the RFC Editor function is currently provided by the Internet Society.</p>
     1435      </div>
    13581436   </body>
    13591437</html>
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