|HTTPbis Working Group||R. Fielding, Editor|
|Obsoletes: 2616 (if approved)||J. Reschke, Editor|
|Updates: 2617 (if approved)||greenbytes|
|Intended status: Standards Track||January 30, 2013|
|Expires: August 3, 2013|
Hypertext Transfer Protocol (HTTP/1.1): Authentication
The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. This document defines the HTTP Authentication framework.
Discussion of this draft takes place on the HTTPBIS working group mailing list (email@example.com), which is archived at <http://lists.w3.org/Archives/Public/ietf-http-wg/>.
The current issues list is at <http://tools.ietf.org/wg/httpbis/trac/report/3> and related documents (including fancy diffs) can be found at <http://tools.ietf.org/wg/httpbis/>.
The changes in this draft are summarized in Appendix D.3.
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This document defines HTTP/1.1 access control and authentication. It includes the relevant parts of RFC 2616 with only minor changes ([RFC2616]), plus the general framework for HTTP authentication, as previously defined in "HTTP Authentication: Basic and Digest Access Authentication" ([RFC2617]).
HTTP provides several OPTIONAL challenge-response authentication mechanisms that 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 RFC 2617.
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 [RFC2119].
Conformance criteria and considerations regarding error handling are defined in Section 2.5 of [Part1].
This specification uses the Augmented Backus-Naur Form (ABNF) notation of [RFC5234] with the list rule extension defined in Section 1.2 of [Part1]. Appendix B describes rules imported from other documents. Appendix C shows the collected ABNF with the list rule expanded.
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.
Parameters are name-value pairs where the name is matched case-insensitively, and each parameter name MUST only occur once per challenge.
auth-scheme = token auth-param = token BWS "=" BWS ( token / quoted-string ) token68 = 1*( ALPHA / DIGIT / "-" / "." / "_" / "~" / "+" / "/" ) *"="
The "token68" syntax allows the 66 unreserved URI characters ([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 ([RFC4648]).
The 401 (Unauthorized) response message is used by an origin server to challenge the authorization of a user agent. This response MUST include a WWW-Authenticate header field containing at least one challenge applicable to the requested resource.
The 407 (Proxy Authentication Required) response message is used by a proxy to challenge the authorization of a client and MUST include a Proxy-Authenticate header field containing at least one challenge applicable to the proxy for the requested resource.
challenge = auth-scheme [ 1*SP ( token68 / #auth-param ) ]
Note: User agents will need to take special care in parsing the WWW-Authenticate and Proxy-Authenticate 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.
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.
A user agent that wishes to authenticate itself with an origin server — usually, but not necessarily, after receiving a 401 (Unauthorized) — can do so by including an Authorization header field with the request.
A client that wishes to authenticate itself with a proxy — usually, but not necessarily, after receiving a 407 (Proxy Authentication Required) — can do so by including a Proxy-Authorization header field with the request.
Both the Authorization field value and the Proxy-Authorization 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.
credentials = auth-scheme [ 1*SP ( token68 / #auth-param ) ]
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 send a 401 (Unauthorized) response that contains a WWW-Authenticate header field with at least one (possibly new) challenge applicable to the requested resource.
Likewise, upon a request that requires authentication by proxies that omit credentials or contain invalid or partial credentials, a proxy SHOULD send a 407 (Proxy Authentication Required) response that contains a Proxy-Authenticate header field with a (possibly new) challenge applicable to the proxy.
A server receiving credentials that are valid, but not adequate to gain access, ought to respond with the 403 (Forbidden) status code (Section 6.5.3 of [Part2]).
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.
Proxies MUST forward the WWW-Authenticate and Authorization header fields unmodified and follow the rules found in Section 4.1.
The authentication parameter realm is reserved for use by authentication schemes that wish to indicate the scope of protection.
A protection space is defined by the canonical root URI (the scheme and authority components of the effective request URI; see Section 5.5 of [Part1]) 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, that can have additional semantics specific to the authentication scheme. Note that there can be multiple challenges with the same auth-scheme but different realms.
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.
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.
The HTTP Authentication Scheme Registry defines the name space for the authentication schemes in challenges and credentials.
Registrations MUST include the following fields:
Values to be added to this name space require IETF Review (see [RFC5226], Section 4.1).
The registry itself is maintained at <http://www.iana.org/assignments/http-authschemes>.
There are certain aspects of the HTTP Authentication Framework that put constraints on how new authentication schemes can work:
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 Section 2.3 of [Part1]).
The authentication parameter "realm" is reserved for defining Protection Spaces as defined in Section 2.2. New schemes MUST NOT use it in a way incompatible with that definition.
The "token68" 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.
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.
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.
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").
The credentials carried in an Authorization 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.
Therefore, new authentication schemes that choose not to carry credentials in the Authorization 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").
The 401 (Unauthorized) status code indicates that the request has not been applied because it lacks valid authentication credentials for the target resource. The origin server MUST send a WWW-Authenticate header field (Section 4.4) containing at least one challenge applicable to the target resource. If the request included authentication credentials, then the 401 response indicates that authorization has been refused for those credentials. The client MAY repeat the request with a new or replaced Authorization header field (Section 4.1). 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 agent SHOULD present the enclosed representation to the user, since it usually contains relevant diagnostic information.
The 407 (Proxy Authentication Required) status code is similar to 401 (Unauthorized), but indicates that the client needs to authenticate itself in order to use a proxy. The proxy MUST send a Proxy-Authenticate header field (Section 4.2) containing a challenge applicable to that proxy for the target resource. The client MAY repeat the request with a new or replaced Proxy-Authorization header field (Section 4.3).
This section defines the syntax and semantics of HTTP/1.1 header fields related to authentication.
The "Authorization" header field allows a user agent to authenticate itself with a server — usually, but not necessarily, after receiving a 401 (Unauthorized) response. Its value consists of credentials containing information of the user agent for the realm of the resource being requested.
Authorization = credentials
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).
See Section 3.2 of [Part6] for details of and requirements pertaining to handling of the Authorization field by HTTP caches.
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 (Section 5.5 of [Part1]). It MUST be included as part of a 407 (Proxy Authentication Required) response.
Proxy-Authenticate = 1#challenge
Unlike WWW-Authenticate, 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.
Note that the parsing considerations for WWW-Authenticate apply to this header field as well; see Section 4.4 for details.
The "Proxy-Authorization" header field allows the client to identify itself (or its user) to a proxy that 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.
Proxy-Authorization = credentials
Unlike Authorization, the Proxy-Authorization header field applies only to the next outbound proxy that demanded authentication using the Proxy-Authenticate 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.
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 (Section 5.5 of [Part1]).
It MUST be included in 401 (Unauthorized) response messages and MAY be included in other response messages to indicate that supplying credentials (or different credentials) might affect the response.
WWW-Authenticate = 1#challenge
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.
WWW-Authenticate: Newauth realm="apps", type=1, title="Login to \"apps\"", Basic realm="simple"
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".
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.
The registration procedure for HTTP Authentication Schemes is defined by Section 2.3 of this document.
The HTTP Method Authentication Scheme shall be created at <http://www.iana.org/assignments/http-authschemes>.
The HTTP Status Code Registry located at <http://www.iana.org/assignments/http-status-codes> shall be updated with the registrations below:
|407||Proxy Authentication Required||Section 3.2|
The Message Header Field Registry located at <http://www.iana.org/assignments/message-headers/message-header-index.html> shall be updated with the permanent registrations below (see [BCP90]):
|Header Field Name||Protocol||Status||Reference|
The change controller is: "IETF (firstname.lastname@example.org) - Internet Engineering Task Force".
This section is meant to inform developers, information providers, and users of known security concerns specific to HTTP/1.1 authentication. More general security considerations are addressed in HTTP messaging [Part1] and semantics [Part2].
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:
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 that mitigate the security problems inherent in this problem. In particular, user agents that cache credentials are encouraged to provide a readily accessible mechanism for discarding cached credentials under user control.
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.
This is of particular concern when a server hosts resources for multiple parties under the same canonical root URI (Section 2.2). Possible mitigation strategies include restricting direct access to authentication credentials (i.e., not making the content of the Authorization request header field available), and separating protection spaces by using a different host name for each party.
This specification takes over the definition of the HTTP Authentication Framework, previously defined in RFC 2617. 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 Section 6 of [RFC2617] for further acknowledgements.
See Section 9 of [Part1] for the Acknowledgments related to this document revision.
|[Part1]||Fielding, R., Ed. and J. Reschke, Ed., “Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing”, Internet-Draft draft-ietf-httpbis-p1-messaging-latest (work in progress), January 2013.|
|[Part2]||Fielding, R., Ed. and J. Reschke, Ed., “Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content”, Internet-Draft draft-ietf-httpbis-p2-semantics-latest (work in progress), January 2013.|
|[Part6]||Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., “Hypertext Transfer Protocol (HTTP/1.1): Caching”, Internet-Draft draft-ietf-httpbis-p6-cache-latest (work in progress), January 2013.|
|[RFC2119]||Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels”, BCP 14, RFC 2119, March 1997.|
|[RFC5234]||Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF”, STD 68, RFC 5234, January 2008.|
|[BCP90]||Klyne, G., Nottingham, M., and J. Mogul, “Registration Procedures for Message Header Fields”, BCP 90, RFC 3864, September 2004.|
|[RFC2616]||Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1”, RFC 2616, June 1999.|
|[RFC2617]||Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, “HTTP Authentication: Basic and Digest Access Authentication”, RFC 2617, June 1999.|
|[RFC3986]||Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifier (URI): Generic Syntax”, STD 66, RFC 3986, January 2005.|
|[RFC4648]||Josefsson, S., “The Base16, Base32, and Base64 Data Encodings”, RFC 4648, October 2006.|
|[RFC5226]||Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs”, BCP 26, RFC 5226, May 2008.|
The framework for HTTP Authentication is now defined by this document, rather than RFC 2617.
The "realm" parameter is no longer always required on challenges; consequently, the ABNF allows challenges without any auth parameters. (Section 2)
The "token68" alternative to auth-param lists has been added for consistency with legacy authentication schemes such as "Basic". (Section 2)
This specification introduces the Authentication Scheme Registry, along with considerations for new authentication schemes. (Section 2.3)
The following core rules are included by reference, as defined in Appendix B.1 of [RFC5234]: 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).
The rules below are defined in [Part1]:
BWS = <BWS, defined in [Part1], Section 3.2.3> OWS = <OWS, defined in [Part1], Section 3.2.3> quoted-string = <quoted-string, defined in [Part1], Section 3.2.6> token = <token, defined in [Part1], Section 3.2.6>
Authorization = credentials BWS = <BWS, defined in [Part1], Section 3.2.3> OWS = <OWS, defined in [Part1], Section 3.2.3> Proxy-Authenticate = *( "," OWS ) challenge *( OWS "," [ OWS challenge ] ) Proxy-Authorization = credentials WWW-Authenticate = *( "," OWS ) challenge *( OWS "," [ OWS challenge ] ) auth-param = token BWS "=" BWS ( token / quoted-string ) auth-scheme = token challenge = auth-scheme [ 1*SP ( token68 / [ ( "," / auth-param ) *( OWS "," [ OWS auth-param ] ) ] ) ] credentials = auth-scheme [ 1*SP ( token68 / [ ( "," / auth-param ) *( OWS "," [ OWS auth-param ] ) ] ) ] quoted-string = <quoted-string, defined in [Part1], Section 3.2.6> token = <token, defined in [Part1], Section 3.2.6> token68 = 1*( ALPHA / DIGIT / "-" / "." / "_" / "~" / "+" / "/" ) *"="
Changes up to the first Working Group Last Call draft are summarized in <http://trac.tools.ietf.org/html/draft-ietf-httpbis-p7-auth-19#appendix-C>.