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.
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Discussion of this draft should take place on the HTTPBIS working group mailing list (firstname.lastname@example.org). 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 B.12.
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 [RFC2617], 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" [RFC2617]. This specification adopts the definitions of "challenge" and "credentials" from that specification.¶
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 Section 1.2 of [Part1] (which extends the syntax defined in [RFC5234] with a list rule). Appendix A shows the collected ABNF, with the list rule expanded.¶
The following core rules are included by reference, as defined in [RFC5234], Appendix 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), VCHAR (any visible USASCII character), and WSP (whitespace).¶
The ABNF rules below are defined in other specifications:¶
The request requires user authentication. The response MUST include a WWW-Authenticate header field (Section 3.4) containing a challenge applicable to the target resource. The client MAY repeat the request with a suitable Authorization header field (Section 3.1). 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. HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication" [RFC2617].¶
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 (Section 3.2) containing a challenge applicable to the proxy for the target resource. The client MAY repeat the request with a suitable Proxy-Authorization header field (Section 3.3). HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication" [RFC2617].¶
This section defines the syntax and semantics of HTTP/1.1 header fields related to authentication.¶
The "Proxy-Authenticate" response-header field consists of a challenge that indicates the authentication scheme and parameters applicable to the proxy for this effective request URI (Section 4.3 of [Part1]). It MUST be included as part of a 407 (Proxy Authentication Required) response.¶
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" [RFC2617]. 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 "WWW-Authenticate" response-header field consists of at least one challenge that indicates the authentication scheme(s) and parameters applicable to the effective request URI (Section 4.3 of [Part1]). It MUST be included in 401 (Unauthorized) response messages.¶
The HTTP access authentication process is described in "HTTP Authentication: Basic and Digest Access Authentication" [RFC2617]. 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 Field Registry located at <http://www.iana.org/assignments/message-headers/message-header-index.html> shall be updated with the permanent registrations below (see [RFC3864]):¶
|Header Field Name||Protocol||Status||Reference|
The change controller is: "IETF (email@example.com) - 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: ¶
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.¶
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>
; Authorization defined but not used ; Proxy-Authenticate defined but not used ; Proxy-Authorization defined but not used ; WWW-Authenticate defined but not used
No significant changes.¶