MAY"> MUST"> MUST NOT"> OPTIONAL"> RECOMMENDED"> REQUIRED"> SHALL"> SHALL NOT"> SHOULD"> SHOULD NOT"> "> "> "> "> ]> HTTP/1.1, part 7: Authentication Day Software
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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). 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. Right now it includes the extracted relevant sections of RFC 2616 with only minor changes. The intention is to move the general framework for HTTP authentication here, as currently specified in , and allow the individual authentication mechanisms to be defined elsewhere. This introduction will be rewritten when that occurs. 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 general framework for access authentication, and the specification of "basic" and "digest" authentication, are specified in "HTTP Authentication: Basic and Digest Access Authentication" . This specification adopts the definitions of "challenge" and "credentials" from that specification.
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;:
OWS = <OWS, defined in &basic-rules;>
The ABNF rules below are defined in other specifications:
challenge = <challenge, defined in > credentials = <credentials, defined in >
The request requires user authentication. The response &MUST; include a WWW-Authenticate header field () containing a challenge applicable to the requested 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 entity that was given in the response, since that entity might include relevant diagnostic information. HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication" .
This code is similar to 401 (Unauthorized), but indicates that the client must first authenticate itself with the proxy. The proxy &MUST; return a Proxy-Authenticate header field () containing a challenge applicable to the proxy for the requested resource. The client &MAY; repeat the request with a suitable Proxy-Authorization header field (). HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication" .
This section defines the syntax and semantics of HTTP/1.1 header fields related to authentication.
A user agent that wishes to authenticate itself with a server-- usually, but not necessarily, after receiving a 401 response--does so by including an Authorization request-header field with the request. The field "Authorization" consists of credentials containing the authentication information of the user agent for the realm of the resource being requested.
Authorization = "Authorization" ":" OWS Authorization-v Authorization-v = credentials
HTTP access authentication is described in "HTTP Authentication: Basic and Digest Access Authentication" . 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 request-headers 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 request-headers 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 response-header field "Proxy-Authenticate" &MUST; be included as part of a 407 (Proxy Authentication Required) response. The field value consists of a challenge that indicates the authentication scheme and parameters applicable to the proxy for this request-target.
Proxy-Authenticate = "Proxy-Authenticate" ":" OWS Proxy-Authenticate-v Proxy-Authenticate-v = 1#challenge
The HTTP access authentication process is described in "HTTP Authentication: Basic and Digest Access Authentication" . 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 request-header field "Proxy-Authorization" allows the client to identify itself (or its user) to a proxy which requires authentication. The Proxy-Authorization field 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 = "Proxy-Authorization" ":" OWS Proxy-Authorization-v Proxy-Authorization-v = credentials
The HTTP access authentication process is described in "HTTP Authentication: Basic and Digest Access Authentication" . 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 response-header field &MUST; be included in 401 (Unauthorized) response messages. The field value consists of at least one challenge that indicates the authentication scheme(s) and parameters applicable to the request-target.
WWW-Authenticate = "WWW-Authenticate" ":" OWS WWW-Authenticate-v WWW-Authenticate-v = 1#challenge
The HTTP access authentication process is described in "HTTP Authentication: Basic and Digest Access Authentication" . 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 Message Header Registry located at should 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.
TBD.
HTTP/1.1, part 1: URIs, Connections, and Message Parsing Day Software
fielding@gbiv.com
 One Laptop per Child
jg@laptop.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 Day Software
fielding@gbiv.com
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JeffMogul@acm.org
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henrikn@microsoft.com
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LMM@acm.org
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paulle@microsoft.com
 World Wide Web Consortium
timbl@w3.org
 World Wide Web Consortium
ylafon@w3.org
 greenbytes GmbH
julian.reschke@greenbytes.de
 Key words for use in RFCs to Indicate Requirement Levels Harvard University
sob@harvard.edu
 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
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 Netscape Communications Corporation Open Market, Inc.
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 Augmented BNF for Syntax Specifications: ABNF Brandenburg InternetWorking
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 THUS plc.
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fielding@ics.uci.edu
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 Compaq Computer Corporation
mogul@wrl.dec.com
 MIT Laboratory for Computer Science
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masinter@parc.xerox.com
 Microsoft Corporation
paulle@microsoft.com
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timbl@w3.org
 Registration Procedures for Message Header Fields Nine by Nine
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JeffMogul@acm.org
Authorization = "Authorization:" OWS Authorization-v Authorization-v = credentials OWS = <OWS, defined in [Part1], Section 1.2.2> Proxy-Authenticate = "Proxy-Authenticate:" OWS Proxy-Authenticate-v Proxy-Authenticate-v = *( "," OWS ) challenge *( OWS "," [ OWS challenge ] ) Proxy-Authorization = "Proxy-Authorization:" OWS Proxy-Authorization-v Proxy-Authorization-v = credentials WWW-Authenticate = "WWW-Authenticate:" OWS WWW-Authenticate-v WWW-Authenticate-v = *( "," OWS ) challenge *( OWS "," [ OWS challenge ] ) challenge = <challenge, defined in [RFC2617], Section 1.2> credentials = <credentials, defined in [RFC2617], Section 1.2>
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
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 Registration (): Reference RFC 3984, and update header registrations for headers 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 value format definitions.
Final work on ABNF conversion (): Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.