MAY"> MUST"> MUST NOT"> OPTIONAL"> RECOMMENDED"> REQUIRED"> SHALL"> SHALL NOT"> SHOULD"> SHOULD NOT"> "> "> "> "> "> "> ]> HTTP/1.1, part 7: Authentication Adobe Systems Incorporated
345 Park Ave San Jose CA 95110 USA fielding@gbiv.com http://roy.gbiv.com/
Alcatel-Lucent Bell Labs
21 Oak Knoll Road Carlisle MA 01741 USA jg@freedesktop.org http://gettys.wordpress.com/
Hewlett-Packard Company
HP Labs, Large Scale Systems Group 1501 Page Mill Road, MS 1177 Palo Alto CA 94304 USA JeffMogul@acm.org
Microsoft Corporation
1 Microsoft Way Redmond WA 98052 USA henrikn@microsoft.com
Adobe Systems Incorporated
345 Park Ave San Jose CA 95110 USA LMM@acm.org http://larry.masinter.net/
Microsoft Corporation
1 Microsoft Way Redmond WA 98052 paulle@microsoft.com
World Wide Web Consortium
MIT Computer Science and Artificial Intelligence Laboratory The Stata Center, Building 32 32 Vassar Street Cambridge MA 02139 USA timbl@w3.org http://www.w3.org/People/Berners-Lee/
World Wide Web Consortium
W3C / ERCIM 2004, rte des Lucioles Sophia-Antipolis AM 06902 France ylafon@w3.org http://www.raubacapeu.net/people/yves/
greenbytes GmbH
Hafenweg 16 MuensterNW48155 Germany +49 251 2807760 +49 251 2807761 julian.reschke@greenbytes.de http://greenbytes.de/tech/webdav/
HTTPbis Working Group 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. Part 7 defines HTTP Authentication. Discussion of this draft should take place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org), which is archived at . The current issues list is at and related documents (including fancy diffs) can be found at . The changes in this draft are summarized in .
This document defines HTTP/1.1 access control and authentication. It includes the relevant parts of RFC 2616 with only minor changes, plus the general framework for HTTP authentication, as previously defined in "HTTP Authentication: Basic and Digest Access Authentication" (). 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 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 . An implementation is not compliant if it fails to satisfy one or more of the "MUST" or "REQUIRED" level requirements for the protocols it implements. An implementation that satisfies all the "MUST" or "REQUIRED" level and all the "SHOULD" level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the "MUST" level requirements but not all the "SHOULD" level requirements for its protocols is said to be "conditionally compliant".
This specification uses the ABNF syntax defined in ¬ation; (which extends the syntax defined in with a list rule). shows the collected ABNF, with the list rule expanded. The following core rules are included by reference, as defined in : 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), VCHAR (any visible USASCII character), and WSP (whitespace).
The core rules below are defined in &basic-rules;:
quoted-string = <quoted-string, defined in &basic-rules;> token = <token, defined in &basic-rules;> OWS = <OWS, defined in &basic-rules;>
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 a comma-separated list of attribute-value pairs which carry the parameters necessary for achieving authentication via that scheme.
auth-scheme = token auth-param = token "=" ( token / quoted-string )
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 1#auth-param
Note: User agents will need to take special care in parsing the WWW-Authenticate or Proxy-Authenticate header field value if it contains more than one challenge, or if more than one WWW-Authenticate header field is provided, since the contents of a challenge can itself contain a comma-separated list of authentication parameters. Note: Many browsers fail to parse challenges containing unknown schemes. A workaround for this problem is to list well-supported schemes (such as "basic") first. The authentication parameter realm is defined for all authentication schemes:
realm = "realm" "=" realm-value realm-value = quoted-string
The realm directive (case-insensitive) is required for all authentication schemes that issue a challenge. The realm value (case-sensitive), in combination with the canonical root URI (the scheme and authority components of the effective request URI; see ) of the server being accessed, defines the protection space. 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. A user agent that wishes to authenticate itself with an origin server — usually, but not necessarily, after receiving a 401 (Unauthorized) — &MAY; 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) — &MAY; do so by including a Proxy-Authorization header field with the request. Both the Authorization field value and the Proxy-Authorization field value consist of credentials containing the authentication information of the client for the realm of the resource being requested. The user agent &MUST; choose to use one of the challenges with the strongest auth-scheme it understands and request credentials from the user based upon that challenge.
credentials = auth-scheme ( token / quoted-string / #auth-param )
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. If the origin server does not wish to accept the credentials sent with a request, it &SHOULD; return a 401 (Unauthorized) response. The response &MUST; include a WWW-Authenticate header field containing at least one (possibly new) challenge applicable to the requested resource. If a proxy does not accept the credentials sent with a request, it &SHOULD; return a 407 (Proxy Authentication Required). The response &MUST; include a Proxy-Authenticate header field containing a (possibly new) challenge applicable to the proxy for the requested resource. 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 headers unmodified and follow the rules found in .
The HTTP Authentication Scheme Registry defines the name space for the authentication schemes in challenges and credentials. Registrations &MUST; include the following fields: Authentication Scheme Name Pointer to specification text Values to be added to this name space are subject to IETF review (). The registry itself is maintained at .
The request requires user authentication. The response &MUST; include a WWW-Authenticate header field () containing a challenge applicable to the target resource. The client &MAY; repeat the request with a suitable Authorization header field (). 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.
This code is similar to 401 (Unauthorized), but indicates that the client ought to first authenticate itself with the proxy. The proxy &MUST; return a Proxy-Authenticate header field () containing a challenge applicable to the proxy for the target resource. The client &MAY; repeat the request with a suitable Proxy-Authorization header field ().
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). 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: 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. 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. If the response includes the "public" cache-control directive, it &MAY; be returned in reply to any subsequent request.
The "Proxy-Authenticate" header field consists of a challenge that indicates the authentication scheme and parameters applicable to the proxy for this effective request URI (&effective-request-uri;). 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 &SHOULD-NOT; be passed on 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.
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.
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 (&effective-request-uri;). It &MUST; be included in 401 (Unauthorized) response messages.
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.
The registration procedure for HTTP Authentication Schemes is defined by of this document. The HTTP Method Authentication Scheme shall be created at .
The HTTP Status Code Registry located at shall be updated with the registrations below: Value Description Reference 401 Unauthorized 407 Proxy Authentication Required
The Message Header Field Registry located at shall be updated with the permanent registrations below (see ): Header Field Name Protocol Status Reference Authorization http standard Proxy-Authenticate http standard Proxy-Authorization http standard WWW-Authenticate http standard The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
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.
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: 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. 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. 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.
This specification takes over the definition of the HTTP Authentication Framework, previously defined in RFC 2617. We thank to 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. HTTPbis acknowledgements.
HTTP/1.1, part 1: URIs, Connections, and Message Parsing Adobe Systems Incorporated
fielding@gbiv.com
 Alcatel-Lucent Bell Labs
jg@freedesktop.org
 Hewlett-Packard Company
JeffMogul@acm.org
 Microsoft Corporation
henrikn@microsoft.com
 Adobe Systems Incorporated
LMM@acm.org
 Microsoft Corporation
paulle@microsoft.com
 World Wide Web Consortium
timbl@w3.org
 World Wide Web Consortium
ylafon@w3.org
 greenbytes GmbH
julian.reschke@greenbytes.de
 HTTP/1.1, part 6: Caching Adobe Systems Incorporated
fielding@gbiv.com
 Alcatel-Lucent Bell Labs
jg@freedesktop.org
 Hewlett-Packard Company
JeffMogul@acm.org
 Microsoft Corporation
henrikn@microsoft.com
 Adobe Systems Incorporated
LMM@acm.org
 Microsoft Corporation
paulle@microsoft.com
 World Wide Web Consortium
timbl@w3.org
 World Wide Web Consortium
ylafon@w3.org
mnot@mnot.net
 greenbytes GmbH
julian.reschke@greenbytes.de
 Key words for use in RFCs to Indicate Requirement Levels Harvard University
sob@harvard.edu
 Augmented BNF for Syntax Specifications: ABNF Brandenburg InternetWorking
dcrocker@bbiw.net
THUS plc.
paul.overell@thus.net
Hypertext Transfer Protocol -- HTTP/1.1 University of California, Irvine
fielding@ics.uci.edu
 W3C
jg@w3.org
 Compaq Computer Corporation
mogul@wrl.dec.com
 MIT Laboratory for Computer Science
frystyk@w3.org
 Xerox Corporation
masinter@parc.xerox.com
 Microsoft Corporation
paulle@microsoft.com
 W3C
timbl@w3.org
 HTTP Authentication: Basic and Digest Access Authentication Northwestern University, Department of Mathematics
john@math.nwu.edu
 Verisign Inc.
pbaker@verisign.com
 AbiSource, Inc.
jeff@AbiSource.com
 Agranat Systems, Inc.
lawrence@agranat.com
 Microsoft Corporation
paulle@microsoft.com
 Netscape Communications Corporation Open Market, Inc.
stewart@OpenMarket.com
 Registration Procedures for Message Header Fields Nine by Nine
GK-IETF@ninebynine.org
 BEA Systems
mnot@pobox.com
 HP Labs
JeffMogul@acm.org
 Guidelines for Writing an IANA Considerations Section in RFCs IBM
narten@us.ibm.com
 Google
Harald@Alvestrand.no
Change ABNF productions for header fields to only define the field value. ()
Authorization = credentials OWS = <OWS, defined in [Part1], Section 1.2.2> Proxy-Authenticate = *( "," OWS ) challenge *( OWS "," [ OWS challenge ] ) Proxy-Authorization = credentials WWW-Authenticate = *( "," OWS ) challenge *( OWS "," [ OWS challenge ] ) auth-param = token "=" ( token / quoted-string ) auth-scheme = token challenge = auth-scheme 1*SP *( "," OWS ) auth-param *( OWS "," [ OWS auth-param ] ) credentials = auth-scheme ( token / quoted-string / [ ( "," / auth-param ) *( OWS "," [ OWS auth-param ] ) ] ) quoted-string = <quoted-string, defined in [Part1], Section 1.2.2> realm = "realm=" realm-value realm-value = quoted-string token = <token, defined in [Part1], Section 1.2.2>
ABNF diagnostics: ; Authorization defined but not used ; Proxy-Authenticate defined but not used ; Proxy-Authorization defined but not used ; WWW-Authenticate defined but not used ; realm defined but not used
Extracted relevant partitions from .
Closed issues: : "Normative and Informative references"
Ongoing work on ABNF conversion (): Explicitly import BNF rules for "challenge" and "credentials" from RFC2617. Add explicit references to BNF syntax and rules imported from other parts of the specification.
Ongoing work on IANA Message Header Field Registration (): Reference RFC 3984, and update header field registrations for header fields defined in this document.
Ongoing work on ABNF conversion (): Use "/" instead of "|" for alternatives. Introduce new ABNF rules for "bad" whitespace ("BWS"), optional whitespace ("OWS") and required whitespace ("RWS"). Rewrite ABNFs to spell out whitespace rules, factor out header field value format definitions.
Final work on ABNF conversion (): Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
None.
Closed issues: : "move IANA registrations for optional status codes"
No significant changes.
Partly resolved issues: : "Term for the requested resource's URI"
None.
Closed issues: : "introduction to part 7 is work-in-progress" : "auth-param syntax" : "Header Classification" : "absorbing the auth framework from 2617" Partly resolved issues: : "should we have an auth scheme registry"
None.
Closed issues: : "untangle ABNFs for header fields"
None.