source: draft-ietf-httpbis/20/p7-auth.xml @ 1807

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<front>

  <title abbrev="HTTP/1.1, Part 7">HTTP/1.1, part 7: Authentication</title>

  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
    <address>
      <postal>
        <street>345 Park Ave</street>
        <city>San Jose</city>
        <region>CA</region>
        <code>95110</code>
        <country>USA</country>
      </postal>
      <email>fielding@gbiv.com</email>
      <uri>http://roy.gbiv.com/</uri>
    </address>
  </author>

  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
    <organization abbrev="W3C">World Wide Web Consortium</organization>
    <address>
      <postal>
        <street>W3C / ERCIM</street>
        <street>2004, rte des Lucioles</street>
        <city>Sophia-Antipolis</city>
        <region>AM</region>
        <code>06902</code>
        <country>France</country>
      </postal>
      <email>ylafon@w3.org</email>
      <uri>http://www.raubacapeu.net/people/yves/</uri>
    </address>
  </author>

  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
    <organization abbrev="greenbytes">greenbytes GmbH</organization>
    <address>
      <postal>
        <street>Hafenweg 16</street>
        <city>Muenster</city><region>NW</region><code>48155</code>
        <country>Germany</country>
      </postal>
      <email>julian.reschke@greenbytes.de</email>
      <uri>http://greenbytes.de/tech/webdav/</uri>
    </address>
  </author>

  <date month="&ID-MONTH;" year="&ID-YEAR;" day="16"/>
  <workgroup>HTTPbis Working Group</workgroup>

<abstract>
<t>
   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
   distributed, collaborative, hypermedia information systems. HTTP has been in
   use by the World Wide Web global information initiative since 1990. This
   document is Part 7 of the seven-part specification that defines the protocol
   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
</t>
<t>
   Part 7 defines the HTTP Authentication framework.
</t>
</abstract>

<note title="Editorial Note (To be removed by RFC Editor)">
  <t>
    Discussion of this draft takes place on the HTTPBIS working group
    mailing list (ietf-http-wg@w3.org), which is archived at
    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
  </t>
  <t>
    The current issues list is at
    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
    documents (including fancy diffs) can be found at
    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
  </t>
  <t>
    The changes in this draft are summarized in <xref target="changes.since.19"/>.
  </t>
</note>
</front>
<middle>
<section title="Introduction" anchor="introduction">
<t>
   This document defines HTTP/1.1 access control and authentication. It
   includes the relevant parts of <xref target="RFC2616" x:fmt="none">RFC 2616</xref>
   with only minor changes (<xref target="RFC2616"/>), plus the general framework for HTTP authentication,
   as previously defined in "HTTP Authentication: Basic and Digest Access
   Authentication" (<xref target="RFC2617"/>).
</t>
<t>
   HTTP provides several &OPTIONAL; challenge-response authentication
   mechanisms which can be used by a server to challenge a client request and
   by a client to provide authentication information. The "basic" and "digest"
   authentication schemes continue to be specified in
   <xref target="RFC2617" x:fmt="none">RFC 2617</xref>.
</t>

<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
<t>
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in <xref target="RFC2119"/>.
</t>
<t>
   This specification targets conformance criteria according to the role of
   a participant in HTTP communication.  Hence, HTTP requirements are placed
   on senders, recipients, clients, servers, user agents, intermediaries,
   origin servers, proxies, gateways, or caches, depending on what behavior
   is being constrained by the requirement. See &architecture; for definitions
   of these terms.
</t>
<t>
   The verb "generate" is used instead of "send" where a requirement
   differentiates between creating a protocol element and merely forwarding a
   received element downstream.
</t>
<t>
   An implementation is considered conformant if it complies with all of the
   requirements associated with the roles it partakes in HTTP. Note that
   SHOULD-level requirements are relevant here, unless one of the documented
   exceptions is applicable.
</t>
<t>
   This document also uses ABNF to define valid protocol elements
   (<xref target="notation"/>).
   In addition to the prose requirements placed upon them, senders &MUST-NOT;
   generate protocol elements that do not match the grammar defined by the
   ABNF rules for those protocol elements that are applicable to the sender's
   role. If a received protocol element is processed, the recipient &MUST; be
   able to parse any value that would match the ABNF rules for that protocol
   element, excluding only those rules not applicable to the recipient's role.
</t>
<t>
   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
   protocol element from an invalid construct.  HTTP does not define
   specific error handling mechanisms except when they have a direct impact
   on security, since different applications of the protocol require
   different error handling strategies.  For example, a Web browser might
   wish to transparently recover from a response where the
   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
   whereas a systems control client might consider any form of error recovery
   to be dangerous.
</t>
</section>

<section title="Syntax Notation" anchor="notation">
<t>
   This specification uses the Augmented Backus-Naur Form (ABNF) notation
   of <xref target="RFC5234"/> with the list rule extension defined in
   &notation;. <xref target="imported.abnf"/> describes rules imported from
   other documents. <xref target="collected.abnf"/> shows the collected ABNF
   with the list rule expanded.
</t>
</section>
</section>

<section title="Access Authentication Framework" anchor="access.authentication.framework">

<section title="Challenge and Response" anchor="challenge.and.response">
  <x:anchor-alias value="auth-scheme"/>
  <x:anchor-alias value="auth-param"/>
  <x:anchor-alias value="b64token"/>
  <x:anchor-alias value="challenge"/>
  <x:anchor-alias value="credentials"/>
<t>
   HTTP provides a simple challenge-response authentication mechanism
   that can be used by a server to challenge a client request and by a
   client to provide authentication information. It uses an extensible,
   case-insensitive token to identify the authentication scheme, followed
   by additional information necessary for achieving authentication via that
   scheme. The latter can either be a comma-separated list of parameters or a
   single sequence of characters capable of holding base64-encoded
   information.
</t>
<t>
   Parameters are name-value pairs where the name is matched case-insensitively,
   and each parameter name &MUST; only occur once per challenge.
</t>
<figure><artwork type="abnf2616"><iref item="auth-scheme" primary="true"/><iref item="auth-param" primary="true"/><iref primary="true" item="Grammar" subitem="auth-scheme"/><iref primary="true" item="Grammar" subitem="auth-param"/><iref item="b64token" primary="true"/><iref primary="true" item="Grammar" subitem="b64token"/>
  auth-scheme    = <x:ref>token</x:ref>
  
  auth-param     = <x:ref>token</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )

  b64token       = 1*( <x:ref>ALPHA</x:ref> / <x:ref>DIGIT</x:ref> /
                       "-" / "." / "_" / "~" / "+" / "/" ) *"=" 
</artwork></figure>
<t>
   The "b64token" syntax allows the 66 unreserved URI characters (<xref target="RFC3986"/>),
   plus a few others, so that it can hold a base64, base64url (URL and filename
   safe alphabet), base32, or base16 (hex) encoding, with or without padding, but
   excluding whitespace (<xref target="RFC4648"/>). 
</t>
<t>
   The <x:ref>401 (Unauthorized)</x:ref> response message is used by an origin server
   to challenge the authorization of a user agent. This response &MUST;
   include a <x:ref>WWW-Authenticate</x:ref> header field containing at least one
   challenge applicable to the requested resource.
</t>
<t>   
   The <x:ref>407 (Proxy Authentication Required)</x:ref> response message is
   used by a proxy to challenge the authorization of a client and &MUST;
   include a <x:ref>Proxy-Authenticate</x:ref> header field containing at least
   one challenge applicable to the proxy for the requested resource.
</t>
<figure><artwork type="abnf2616"><iref item="challenge" primary="true"/><iref primary="true" item="Grammar" subitem="challenge"/>
  <x:ref>challenge</x:ref>   = <x:ref>auth-scheme</x:ref> [ 1*<x:ref>SP</x:ref> ( <x:ref>b64token</x:ref> / #<x:ref>auth-param</x:ref> ) ]
</artwork></figure>
<x:note>
  <t>
     &Note; User agents will need to take special care in parsing the
     <x:ref>WWW-Authenticate</x:ref> and <x:ref>Proxy-Authenticate</x:ref>
     header field values because they can contain more than one challenge, or
     if more than one of each is provided, since the contents of a challenge
     can itself contain a comma-separated list of authentication parameters.
  </t>
</x:note>
<x:note>
  <t>
     &Note; Many clients fail to parse challenges containing unknown
     schemes. A workaround for this problem is to list well-supported schemes
     (such as "basic") first.<!-- see http://greenbytes.de/tech/tc/httpauth/#multibasicunknown2 -->
  </t>
</x:note>
<t>
   A user agent that wishes to authenticate itself with an origin server
   &mdash; usually, but not necessarily, after receiving a <x:ref>401 (Unauthorized)</x:ref>
   &mdash; can do so by including an <x:ref>Authorization</x:ref> header field with the
   request.
</t>
<t>   
   A client that wishes to authenticate itself with a proxy &mdash; usually,
   but not necessarily, after receiving a <x:ref>407 (Proxy Authentication Required)</x:ref>
   &mdash; can do so by including a <x:ref>Proxy-Authorization</x:ref> header field with the
   request.
</t>
<t>
   Both the <x:ref>Authorization</x:ref> field value and the <x:ref>Proxy-Authorization</x:ref> field value
   contain the client's credentials for the realm of the resource being
   requested, based upon a challenge received from the server (possibly at
   some point in the past). When creating their values, the user agent ought to
   do so by selecting the challenge with what it considers to be the most
   secure auth-scheme that it understands, obtaining credentials from the user
   as appropriate.
</t>
<figure><artwork type="abnf2616"><iref item="credentials" primary="true"/><iref primary="true" item="Grammar" subitem="credentials"/>
  <x:ref>credentials</x:ref> = <x:ref>auth-scheme</x:ref> [ 1*<x:ref>SP</x:ref> ( <x:ref>b64token</x:ref> / #<x:ref>auth-param</x:ref> ) ]
</artwork></figure>
<t>
   Upon a request for a protected resource that omits credentials, contains
   invalid credentials (e.g., a bad password) or partial credentials (e.g.,
   when the authentication scheme requires more than one round trip), an origin
   server &SHOULD; return a <x:ref>401 (Unauthorized)</x:ref> response. Such
   responses &MUST; include a <x:ref>WWW-Authenticate</x:ref> header field
   containing at least one (possibly new) challenge applicable to the
   requested resource.
</t>
<t>
   Likewise, upon a request that requires authentication by proxies that omit
   credentials or contain invalid or partial credentials, a proxy &SHOULD;
   return a <x:ref>407 (Proxy Authentication Required)</x:ref> response. Such responses
   &MUST; include a <x:ref>Proxy-Authenticate</x:ref> header field containing a (possibly
   new) challenge applicable to the proxy.
</t>
<t>
   A server receiving credentials that are valid, but not adequate to gain
   access, ought to respond with the <x:ref>403 (Forbidden)</x:ref> status code (&status.403;).
</t>
<t>
   The HTTP protocol does not restrict applications to this simple
   challenge-response mechanism for access authentication. Additional
   mechanisms &MAY; be used, such as encryption at the transport level or
   via message encapsulation, and with additional header fields
   specifying authentication information. However, such additional
   mechanisms are not defined by this specification.
</t>
<t>
   Proxies &MUST; forward the <x:ref>WWW-Authenticate</x:ref> and
   <x:ref>Authorization</x:ref> header fields unmodified and follow the rules
   found in <xref target="header.authorization"/>.
</t>
</section>

<section title="Protection Space (Realm)" anchor="protection.space">
  <iref item="Protection Space"/>
  <iref item="Realm"/>
  <iref item="Canonical Root URI"/>
<t>
   The authentication parameter realm is reserved for use by authentication
   schemes that wish to indicate the scope of protection.
</t>
<t>
   A <x:dfn>protection space</x:dfn> is defined by the canonical root URI (the
   scheme and authority components of the effective request URI; see
   <xref target="Part1" x:fmt="of" x:rel="#effective.request.uri"/>) of the
   server being accessed, in combination with the realm value if present.
   These realms allow the protected resources on a server to be
   partitioned into a set of protection spaces, each with its own
   authentication scheme and/or authorization database. The realm value
   is a string, generally assigned by the origin server, which can have
   additional semantics specific to the authentication scheme. Note that
   there can be multiple challenges with the same auth-scheme but
   different realms.
</t>
<t>
   The protection space determines the domain over which credentials can
   be automatically applied. If a prior request has been authorized, the
   same credentials &MAY; be reused for all other requests within that
   protection space for a period of time determined by the
   authentication scheme, parameters, and/or user preference. Unless
   otherwise defined by the authentication scheme, a single protection
   space cannot extend outside the scope of its server.
</t>
<t>
   For historical reasons, senders &MUST; only use the quoted-string syntax.
   Recipients might have to support both token and quoted-string syntax for
   maximum interoperability with existing clients that have been accepting both
   notations for a long time.
</t>
</section>

<section title="Authentication Scheme Registry" anchor="authentication.scheme.registry">
<t>
  The HTTP Authentication Scheme Registry defines the name space for the
  authentication schemes in challenges and credentials.
</t>
<t>
  Registrations &MUST; include the following fields:
  <list style="symbols">
    <t>Authentication Scheme Name</t>
    <t>Pointer to specification text</t>
    <t>Notes (optional)</t>
  </list>
</t>
<t>
  Values to be added to this name space require IETF Review
  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
</t>
<t>
  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-authschemes"/>.
</t>

<section title="Considerations for New Authentication Schemes" anchor="considerations.for.new.authentication.schemes">
<t>
  There are certain aspects of the HTTP Authentication Framework that put
  constraints on how new authentication schemes can work:
</t>
<t>
  <list style="symbols">
    <x:lt>
    <t>
      HTTP authentication is presumed to be stateless: all of the information
      necessary to authenticate a request &MUST; be provided in the request,
      rather than be dependent on the server remembering prior requests.
      Authentication based on, or bound to, the underlying connection is
      outside the scope of this specification and inherently flawed unless
      steps are taken to ensure that the connection cannot be used by any
      party other than the authenticated user
      (see &msg-orient-and-buffering;). 
    </t>
    </x:lt>
    <x:lt>
    <t>
      The authentication parameter "realm" is reserved for defining Protection
      Spaces as defined in <xref target="protection.space"/>. New schemes
      &MUST-NOT; use it in a way incompatible with that definition.
    </t>
    </x:lt>
    <x:lt>
    <t>
      The "b64token" notation was introduced for compatibility with existing
      authentication schemes and can only be used once per challenge/credentials.
      New schemes thus ought to use the "auth-param" syntax instead, because
      otherwise future extensions will be impossible.
    </t>
    </x:lt>
    <x:lt>
    <t>
      The parsing of challenges and credentials is defined by this specification,
      and cannot be modified by new authentication schemes. When the auth-param
      syntax is used, all parameters ought to support both token and
      quoted-string syntax, and syntactical constraints ought to be defined on
      the field value after parsing (i.e., quoted-string processing). This is
      necessary so that recipients can use a generic parser that applies to
      all authentication schemes.
    </t>
    <t>
      &Note; The fact that the value syntax for the "realm" parameter
      is restricted to quoted-string was a bad design choice not to be repeated
      for new parameters.
    </t>
    </x:lt>
    <x:lt>
    <t>
      Definitions of new schemes ought to define the treatment of unknown
      extension parameters. In general, a "must-ignore" rule is preferable
      over "must-understand", because otherwise it will be hard to introduce
      new parameters in the presence of legacy recipients. Furthermore,
      it's good to describe the policy for defining new parameters (such
      as "update the specification", or "use this registry"). 
    </t>
    </x:lt>
    <x:lt>
    <t>
      Authentication schemes need to document whether they are usable in
      origin-server authentication (i.e., using <x:ref>WWW-Authenticate</x:ref>),
      and/or proxy authentication (i.e., using <x:ref>Proxy-Authenticate</x:ref>).
    </t>
    </x:lt>
    <x:lt>
    <t>
      The credentials carried in an <x:ref>Authorization</x:ref> header field are specific to
      the User Agent, and therefore have the same effect on HTTP caches as the
      "private" Cache-Control response directive, within the scope of the
      request they appear in.
    </t>
    <t>
      Therefore, new authentication schemes which choose not to carry
      credentials in the <x:ref>Authorization</x:ref> header field (e.g., using a newly defined
      header field) will need to explicitly disallow caching, by mandating the use of
      either Cache-Control request directives (e.g., "no-store") or response
      directives (e.g., "private").
    </t>
    </x:lt>
  </list>
</t>
</section>

</section>

</section>

<section title="Status Code Definitions" anchor="status.code.definitions">
<section title="401 Unauthorized" anchor="status.401">
  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
  <x:anchor-alias value="401 (Unauthorized)"/>
<t>
   The request requires user authentication. The response &MUST; include a
   <x:ref>WWW-Authenticate</x:ref> header field (<xref target="header.www-authenticate"/>)
   containing a challenge applicable to the target resource. The client &MAY;
   repeat the request with a suitable <x:ref>Authorization</x:ref> header field
   (<xref target="header.authorization"/>). If the request already included
   Authorization credentials, then the 401 response indicates that authorization
   has been refused for those credentials. If the 401 response contains the
   same challenge as the prior response, and the user agent has already attempted
   authentication at least once, then the user &SHOULD; be presented the
   representation that was given in the response, since that representation might
   include relevant diagnostic information.
</t>
</section>
<section title="407 Proxy Authentication Required" anchor="status.407">
  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
  <x:anchor-alias value="407 (Proxy Authentication Required)"/>
<t>
   This code is similar to <x:ref>401 (Unauthorized)</x:ref>, but indicates that the
   client ought to first authenticate itself with the proxy. The proxy &MUST;
   return a <x:ref>Proxy-Authenticate</x:ref> header field (<xref target="header.proxy-authenticate"/>) containing a
   challenge applicable to the proxy for the target resource. The
   client &MAY; repeat the request with a suitable <x:ref>Proxy-Authorization</x:ref>
   header field (<xref target="header.proxy-authorization"/>).
</t>
</section>
</section>

<section title="Header Field Definitions" anchor="header.field.definitions">
<t>
   This section defines the syntax and semantics of HTTP/1.1 header fields
   related to authentication.
</t>

<section title="Authorization" anchor="header.authorization">
  <iref primary="true" item="Authorization header field" x:for-anchor=""/>
  <iref primary="true" item="Header Fields" subitem="Authorization" x:for-anchor=""/>
  <x:anchor-alias value="Authorization"/>
<t>
   The "Authorization" header field allows a user agent to authenticate
   itself with a server &mdash; usually, but not necessarily, after receiving a <x:ref>401
   (Unauthorized)</x:ref> response. Its value consists of credentials containing 
   information of the user agent for the realm of the resource being
   requested.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Authorization"/>
  <x:ref>Authorization</x:ref> = <x:ref>credentials</x:ref>
</artwork></figure>
<t>
   If a request is
   authenticated and a realm specified, the same credentials &SHOULD;
   be valid for all other requests within this realm (assuming that
   the authentication scheme itself does not require otherwise, such
   as credentials that vary according to a challenge value or using
   synchronized clocks).
</t>
<t>
      When a shared cache (see &shared-and-non-shared-caches;) receives a request
      containing an Authorization field, it &MUST-NOT; return the
      corresponding response as a reply to any other request, unless one
      of the following specific exceptions holds:
</t>
<t>
  <list style="numbers">
      <t>If the response includes the "s-maxage" cache-control
         directive, the cache &MAY; use that response in replying to a
         subsequent request. But (if the specified maximum age has
         passed) a proxy cache &MUST; first revalidate it with the origin
         server, using the header fields from the new request to allow
         the origin server to authenticate the new request. (This is the
         defined behavior for s-maxage.) If the response includes "s-maxage=0",
         the proxy &MUST; always revalidate it before re-using
         it.</t>

      <t>If the response includes the "must-revalidate" cache-control
         directive, the cache &MAY; use that response in replying to a
         subsequent request. But if the response is stale, all caches
         &MUST; first revalidate it with the origin server, using the
         header fields from the new request to allow the origin server
         to authenticate the new request.</t>

      <t>If the response includes the "public" cache-control directive,
         it &MAY; be returned in reply to any subsequent request.</t>
  </list>
</t>
</section>

<section title="Proxy-Authenticate" anchor="header.proxy-authenticate">
  <iref primary="true" item="Proxy-Authenticate header field" x:for-anchor=""/>
  <iref primary="true" item="Header Fields" subitem="Proxy-Authenticate" x:for-anchor=""/>
  <x:anchor-alias value="Proxy-Authenticate"/>
<t>
   The "Proxy-Authenticate" header field consists of at least one
   challenge that indicates the authentication scheme(s) and parameters
   applicable to the proxy for this effective request URI (&effective-request-uri;).
   It &MUST; be included as part of a <x:ref>407 (Proxy Authentication Required)</x:ref> response.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Proxy-Authenticate"/>
  <x:ref>Proxy-Authenticate</x:ref> = 1#<x:ref>challenge</x:ref>
</artwork></figure>
<t>
   Unlike <x:ref>WWW-Authenticate</x:ref>, the Proxy-Authenticate header field
   applies only to the current connection, and intermediaries &SHOULD-NOT;
   forward it to downstream clients. However, an intermediate proxy might need
   to obtain its own credentials by requesting them from the downstream client,
   which in some circumstances will appear as if the proxy is forwarding the
   Proxy-Authenticate header field.
</t>
<t>
   Note that the parsing considerations for <x:ref>WWW-Authenticate</x:ref>
   apply to this header field as well; see <xref target="header.www-authenticate"/>
   for details.
</t>
</section>

<section title="Proxy-Authorization" anchor="header.proxy-authorization">
  <iref primary="true" item="Proxy-Authorization header field" x:for-anchor=""/>
  <iref primary="true" item="Header Fields" subitem="Proxy-Authorization" x:for-anchor=""/>
  <x:anchor-alias value="Proxy-Authorization"/>
<t>
   The "Proxy-Authorization" header field allows the client to
   identify itself (or its user) to a proxy which requires
   authentication. Its value consists of
   credentials containing the authentication information of the user
   agent for the proxy and/or realm of the resource being requested.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Proxy-Authorization"/>
  <x:ref>Proxy-Authorization</x:ref> = <x:ref>credentials</x:ref>
</artwork></figure>
<t>
   Unlike <x:ref>Authorization</x:ref>, the Proxy-Authorization header field applies only to
   the next outbound proxy that demanded authentication using the <x:ref>Proxy-Authenticate</x:ref>
   field. When multiple proxies are used in a chain, the
   Proxy-Authorization header field is consumed by the first outbound
   proxy that was expecting to receive credentials. A proxy &MAY; relay
   the credentials from the client request to the next proxy if that is
   the mechanism by which the proxies cooperatively authenticate a given
   request.
</t>
</section>

<section title="WWW-Authenticate" anchor="header.www-authenticate">
  <iref primary="true" item="WWW-Authenticate header field" x:for-anchor=""/>
  <iref primary="true" item="Header Fields" subitem="WWW-Authenticate" x:for-anchor=""/>
  <x:anchor-alias value="WWW-Authenticate"/>
<t>
   The "WWW-Authenticate" header field consists of at least one
   challenge that indicates the authentication scheme(s) and parameters
   applicable to the effective request URI (&effective-request-uri;).
</t>
<t>   
   It &MUST; be included in <x:ref>401 (Unauthorized)</x:ref> response messages and &MAY; be
   included in other response messages to indicate that supplying credentials
   (or different credentials) might affect the response.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="WWW-Authenticate"/>
  <x:ref>WWW-Authenticate</x:ref> = 1#<x:ref>challenge</x:ref>
</artwork></figure>
<t>
   User agents are advised to take special care in parsing the WWW-Authenticate
   field value as it might contain more than one challenge,
   or if more than one WWW-Authenticate header field is provided, the
   contents of a challenge itself can contain a comma-separated list of
   authentication parameters.
</t>
<figure>
  <preamble>For instance:</preamble>
  <artwork type="example">
  WWW-Authenticate: Newauth realm="apps", type=1,
                    title="Login to \"apps\"", Basic realm="simple"
</artwork>
  <postamble>
  This header field contains two challenges; one for the "Newauth" scheme
  with a realm value of "apps", and two additional parameters "type" and
  "title", and another one for the "Basic" scheme with a realm value of
  "simple".
</postamble></figure>
<x:note>
  <t>
    &Note; The challenge grammar production uses the list syntax as 
    well. Therefore, a sequence of comma, whitespace, and comma can be
    considered both as applying to the preceding challenge, or to be an
    empty entry in the list of challenges. In practice, this ambiguity
    does not affect the semantics of the header field value and thus is
    harmless.
  </t>
</x:note>
</section>

</section>

<section title="IANA Considerations" anchor="IANA.considerations">

<section title="Authentication Scheme Registry" anchor="authentication.scheme.registration">
<t>
  The registration procedure for HTTP Authentication Schemes is defined by 
  <xref target="authentication.scheme.registry"/> of this document.
</t>
<t>
   The HTTP Method Authentication Scheme shall be created at <eref target="http://www.iana.org/assignments/http-authschemes"/>.
</t>
</section>

<section title="Status Code Registration" anchor="status.code.registration">
<t>
   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
   shall be updated with the registrations below:
</t>
<?BEGININC p7-auth.iana-status-codes ?>
<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
   <ttcol>Value</ttcol>
   <ttcol>Description</ttcol>
   <ttcol>Reference</ttcol>
   <c>401</c>
   <c>Unauthorized</c>
   <c>
      <xref target="status.401"/>
   </c>
   <c>407</c>
   <c>Proxy Authentication Required</c>
   <c>
      <xref target="status.407"/>
   </c>
</texttable>
<!--(END)-->
<?ENDINC p7-auth.iana-status-codes ?>
</section>

<section title="Header Field Registration" anchor="header.field.registration">
<t>
   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
   with the permanent registrations below (see <xref target="RFC3864"/>):
</t>
<?BEGININC p7-auth.iana-headers ?>
<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
   <ttcol>Header Field Name</ttcol>
   <ttcol>Protocol</ttcol>
   <ttcol>Status</ttcol>
   <ttcol>Reference</ttcol>

   <c>Authorization</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.authorization"/>
   </c>
   <c>Proxy-Authenticate</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.proxy-authenticate"/>
   </c>
   <c>Proxy-Authorization</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.proxy-authorization"/>
   </c>
   <c>WWW-Authenticate</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.www-authenticate"/>
   </c>
</texttable>
<!--(END)-->
<?ENDINC p7-auth.iana-headers ?>
<t>
   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
</t>
</section>
</section>

<section title="Security Considerations" anchor="security.considerations">
<t>
   This section is meant to inform application developers, information
   providers, and users of the security limitations in HTTP/1.1 as
   described by this document. The discussion does not include
   definitive solutions to the problems revealed, though it does make
   some suggestions for reducing security risks.
</t>

<section title="Authentication Credentials and Idle Clients" anchor="auth.credentials.and.idle.clients">
<t>
   Existing HTTP clients and user agents typically retain authentication
   information indefinitely. HTTP/1.1 does not provide a method for a
   server to direct clients to discard these cached credentials. This is
   a significant defect that requires further extensions to HTTP.
   Circumstances under which credential caching can interfere with the
   application's security model include but are not limited to:
  <list style="symbols">
     <t>Clients which have been idle for an extended period following
        which the server might wish to cause the client to reprompt the
        user for credentials.</t>

     <t>Applications which include a session termination indication
        (such as a "logout" or "commit" button on a page) after which
        the server side of the application "knows" that there is no
        further reason for the client to retain the credentials.</t>
  </list>
</t>
<t>
   This is currently under separate study. There are a number of work-arounds
   to parts of this problem, and we encourage the use of
   password protection in screen savers, idle time-outs, and other
   methods which mitigate the security problems inherent in this
   problem. In particular, user agents which cache credentials are
   encouraged to provide a readily accessible mechanism for discarding
   cached credentials under user control.
</t>
</section>

<section title="Protection Spaces" anchor="protection.spaces">
<t>
  Authentication schemes that solely rely on the "realm" mechanism for
  establishing a protection space will expose credentials to all resources on a
  server. Clients that have successfully made authenticated requests with a
  resource can use the same authentication credentials for other resources on
  the same server. This makes it possible for a different resource to harvest
  authentication credentials for other resources.
</t>
<t>
  This is of particular concern when a server hosts resources for multiple
  parties under the same canonical root URI (<xref target="protection.space"/>).
  Possible mitigation strategies include restricting direct access to
  authentication credentials (i.e., not making the content of the
  <x:ref>Authorization</x:ref> request header field available), and separating protection
  spaces by using a different host name for each party.
</t>
</section>
</section>

<section title="Acknowledgments" anchor="acks">
<t>
  This specification takes over the definition of the HTTP Authentication
  Framework, previously defined in <xref target="RFC2617" x:fmt="none">RFC 2617</xref>.
  We thank John Franks, Phillip M. Hallam-Baker, Jeffery L. Hostetler, Scott D. Lawrence,
  Paul J. Leach, Ari Luotonen, and Lawrence C. Stewart for their work
  on that specification. See <xref target="RFC2617" x:fmt="of" x:sec="6"/>
  for further acknowledgements.  
</t>
<t>
  See &acks; for the Acknowledgments related to this document revision.
</t>
</section>
</middle>

<back>

<references title="Normative References">

<reference anchor="Part1">
  <front>
    <title>HTTP/1.1, part 1: Message Routing and Syntax"</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
      <organization abbrev="W3C">World Wide Web Consortium</organization>
      <address><email>ylafon@w3.org</email></address>
    </author>
    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
      <organization abbrev="greenbytes">greenbytes GmbH</organization>
      <address><email>julian.reschke@greenbytes.de</email></address>
    </author>
    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
</reference>

<reference anchor="Part2">
  <front>
    <title>HTTP/1.1, part 2: Semantics and Payloads</title>
    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
      <organization abbrev="W3C">World Wide Web Consortium</organization>
      <address><email>ylafon@w3.org</email></address>
    </author>
    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
      <organization abbrev="greenbytes">greenbytes GmbH</organization>
      <address><email>julian.reschke@greenbytes.de</email></address>
    </author>
    <date month="&ID-MONTH;" year="&ID-YEAR;" />
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;" />
  <x:source basename="p2-semantics" href="p2-semantics.xml">
    <x:defines>403 (Forbidden)</x:defines>
    <x:defines>Location</x:defines>
  </x:source>
</reference>

<reference anchor="Part6">
  <front>
    <title>HTTP/1.1, part 6: Caching</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
      <organization abbrev="W3C">World Wide Web Consortium</organization>
      <address><email>ylafon@w3.org</email></address>
    </author>
    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
      <organization>Rackspace</organization>
      <address><email>mnot@mnot.net</email></address>
    </author>
    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
      <organization abbrev="greenbytes">greenbytes GmbH</organization>
      <address><email>julian.reschke@greenbytes.de</email></address>
    </author>
    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
  <x:source href="p6-cache.xml" basename="p6-cache"/>
</reference>

<reference anchor="RFC2119">
  <front>
    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
    <author initials="S." surname="Bradner" fullname="Scott Bradner">
      <organization>Harvard University</organization>
      <address><email>sob@harvard.edu</email></address>
    </author>
    <date month="March" year="1997"/>
  </front>
  <seriesInfo name="BCP" value="14"/>
  <seriesInfo name="RFC" value="2119"/>
</reference>

<reference anchor="RFC5234">
  <front>
    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
      <organization>Brandenburg InternetWorking</organization>
      <address>
        <email>dcrocker@bbiw.net</email>
      </address>  
    </author>
    <author initials="P." surname="Overell" fullname="Paul Overell">
      <organization>THUS plc.</organization>
      <address>
        <email>paul.overell@thus.net</email>
      </address>
    </author>
    <date month="January" year="2008"/>
  </front>
  <seriesInfo name="STD" value="68"/>
  <seriesInfo name="RFC" value="5234"/>
</reference>

</references>

<references title="Informative References">

<reference anchor="RFC2616">
  <front>
    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
    <author initials="R." surname="Fielding" fullname="R. Fielding">
      <organization>University of California, Irvine</organization>
      <address><email>fielding@ics.uci.edu</email></address>
    </author>
    <author initials="J." surname="Gettys" fullname="J. Gettys">
      <organization>W3C</organization>
      <address><email>jg@w3.org</email></address>
    </author>
    <author initials="J." surname="Mogul" fullname="J. Mogul">
      <organization>Compaq Computer Corporation</organization>
      <address><email>mogul@wrl.dec.com</email></address>
    </author>
    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
      <organization>MIT Laboratory for Computer Science</organization>
      <address><email>frystyk@w3.org</email></address>
    </author>
    <author initials="L." surname="Masinter" fullname="L. Masinter">
      <organization>Xerox Corporation</organization>
      <address><email>masinter@parc.xerox.com</email></address>
    </author>
    <author initials="P." surname="Leach" fullname="P. Leach">
      <organization>Microsoft Corporation</organization>
      <address><email>paulle@microsoft.com</email></address>
    </author>
    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
      <organization>W3C</organization>
      <address><email>timbl@w3.org</email></address>
    </author>
    <date month="June" year="1999"/>
  </front>
  <seriesInfo name="RFC" value="2616"/>
</reference>

<reference anchor="RFC2617">
  <front>
    <title abbrev="HTTP Authentication">HTTP Authentication: Basic and Digest Access Authentication</title>
    <author initials="J." surname="Franks" fullname="John Franks">
      <organization>Northwestern University, Department of Mathematics</organization>
      <address><email>john@math.nwu.edu</email></address>
    </author>
    <author initials="P.M." surname="Hallam-Baker" fullname="Phillip M. Hallam-Baker">
      <organization>Verisign Inc.</organization>
      <address><email>pbaker@verisign.com</email></address>
    </author>
    <author initials="J.L." surname="Hostetler" fullname="Jeffery L. Hostetler">
      <organization>AbiSource, Inc.</organization>
      <address><email>jeff@AbiSource.com</email></address>
    </author>
    <author initials="S.D." surname="Lawrence" fullname="Scott D. Lawrence">
      <organization>Agranat Systems, Inc.</organization>
      <address><email>lawrence@agranat.com</email></address>
    </author>
    <author initials="P.J." surname="Leach" fullname="Paul J. Leach">
      <organization>Microsoft Corporation</organization>
      <address><email>paulle@microsoft.com</email></address>
    </author>
    <author initials="A." surname="Luotonen" fullname="Ari Luotonen">
      <organization>Netscape Communications Corporation</organization>
    </author>
    <author initials="L." surname="Stewart" fullname="Lawrence C. Stewart">
      <organization>Open Market, Inc.</organization>
      <address><email>stewart@OpenMarket.com</email></address>
    </author>
    <date month="June" year="1999"/>
  </front>
  <seriesInfo name="RFC" value="2617"/>
</reference>

<reference anchor='RFC3864'>
  <front>
    <title>Registration Procedures for Message Header Fields</title>
    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
      <organization>Nine by Nine</organization>
      <address><email>GK-IETF@ninebynine.org</email></address>
    </author>
    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
      <organization>BEA Systems</organization>
      <address><email>mnot@pobox.com</email></address>
    </author>
    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
      <organization>HP Labs</organization>
      <address><email>JeffMogul@acm.org</email></address>
    </author>
    <date year='2004' month='September' />
  </front>
  <seriesInfo name='BCP' value='90' />
  <seriesInfo name='RFC' value='3864' />
</reference>

<reference anchor="RFC3986">
 <front>
  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
    <address>
       <email>timbl@w3.org</email>
       <uri>http://www.w3.org/People/Berners-Lee/</uri>
    </address>
  </author>
  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
    <organization abbrev="Day Software">Day Software</organization>
    <address>
      <email>fielding@gbiv.com</email>
      <uri>http://roy.gbiv.com/</uri>
    </address>
  </author>
  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
    <address>
      <email>LMM@acm.org</email>
      <uri>http://larry.masinter.net/</uri>
    </address>
  </author>
  <date month='January' year='2005'></date>
 </front>
 <seriesInfo name="STD" value="66"/>
 <seriesInfo name="RFC" value="3986"/>
</reference>

<reference anchor="RFC4648">
  <front>
    <title>The Base16, Base32, and Base64 Data Encodings</title>
    <author fullname="S. Josefsson" initials="S." surname="Josefsson"/>
    <date year="2006" month="October"/>
  </front>
  <seriesInfo value="4648" name="RFC"/>
</reference>

<reference anchor='RFC5226'>
  <front>
    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
    <author initials='T.' surname='Narten' fullname='T. Narten'>
      <organization>IBM</organization>
      <address><email>narten@us.ibm.com</email></address>
    </author>
    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
      <organization>Google</organization>
      <address><email>Harald@Alvestrand.no</email></address>
    </author>
    <date year='2008' month='May' />
  </front>
  <seriesInfo name='BCP' value='26' />
  <seriesInfo name='RFC' value='5226' />
</reference>

</references>

<section title="Changes from RFCs 2616 and 2617" anchor="changes.from.rfc.2616">
<t>
  The "realm" parameter isn't required anymore in general; consequently, the
  ABNF allows challenges without any auth parameters.
  (<xref target="access.authentication.framework"/>)
</t>
<t>
  The "b64token" alternative to auth-param lists has been added for consistency
  with legacy authentication schemes such as "Basic".
  (<xref target="access.authentication.framework"/>)
</t>
<t>
  Introduce Authentication Scheme Registry.
  (<xref target="authentication.scheme.registry"/>)
</t>
<t>
  Change ABNF productions for header fields to only define the field value.
  (<xref target="header.field.definitions"/>)
</t>
</section>
 
<section title="Imported ABNF" anchor="imported.abnf">
  <x:anchor-alias value="ALPHA"/>
  <x:anchor-alias value="CR"/>
  <x:anchor-alias value="DIGIT"/>
  <x:anchor-alias value="LF"/>
  <x:anchor-alias value="OCTET"/>
  <x:anchor-alias value="VCHAR"/>
  <x:anchor-alias value="SP"/>
  <x:anchor-alias value="quoted-string"/>
  <x:anchor-alias value="token"/>
  <x:anchor-alias value="BWS"/>
  <x:anchor-alias value="OWS"/>
<t>
  The following core rules are included by
  reference, as defined in <xref target="RFC5234" x:fmt="of" x:sec="B.1"/>:
  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
  DIGIT (decimal 0-9), DQUOTE (double quote),
  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
  OCTET (any 8-bit sequence of data), SP (space), and
  VCHAR (any visible US-ASCII character).
</t>
<t>
   The rules below are defined in <xref target="Part1"/>:
</t>
<figure><artwork type="abnf2616">
  <x:ref>BWS</x:ref>           = &lt;BWS, defined in &whitespace;&gt;
  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &whitespace;&gt;
  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-components;&gt;
  <x:ref>token</x:ref>         = &lt;token, defined in &field-components;&gt;
</artwork></figure>
</section> 

<?BEGININC p7-auth.abnf-appendix ?>
<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
<figure>
<artwork type="abnf" name="p7-auth.parsed-abnf">
<x:ref>Authorization</x:ref> = credentials

<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;

<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;

<x:ref>Proxy-Authenticate</x:ref> = *( "," OWS ) challenge *( OWS "," [ OWS
 challenge ] )
<x:ref>Proxy-Authorization</x:ref> = credentials

<x:ref>WWW-Authenticate</x:ref> = *( "," OWS ) challenge *( OWS "," [ OWS challenge
 ] )

<x:ref>auth-param</x:ref> = token BWS "=" BWS ( token / quoted-string )
<x:ref>auth-scheme</x:ref> = token

<x:ref>b64token</x:ref> = 1*( ALPHA / DIGIT / "-" / "." / "_" / "~" / "+" / "/" )
 *"="

<x:ref>challenge</x:ref> = auth-scheme [ 1*SP ( b64token / [ ( "," / auth-param ) *(
 OWS "," [ OWS auth-param ] ) ] ) ]
<x:ref>credentials</x:ref> = auth-scheme [ 1*SP ( b64token / [ ( "," / auth-param )
 *( OWS "," [ OWS auth-param ] ) ] ) ]

<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;

<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
</artwork>
</figure>
</section>
<?ENDINC p7-auth.abnf-appendix ?>

<section title="Change Log (to be removed by RFC Editor before publication)"  anchor="change.log">
<t>
  Changes up to the first Working Group Last Call draft are summarized
  in <eref target="http://trac.tools.ietf.org/html/draft-ietf-httpbis-p7-auth-19#appendix-C"/>.
</t>

<section title="Since draft-ietf-httpbis-p7-auth-19" anchor="changes.since.19">
<t>
  Closed issues:
  <list style="symbols">
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/348"/>:
      "Realms and scope"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/349"/>:
      "Strength"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/357"/>:
      "Authentication exchanges"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
      "ABNF requirements for recipients"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/368"/>:
      "note introduction of new IANA registries as normative changes"
    </t>
  </list>
</t>
</section>

</section>

</back>
</rfc>