HTTP/1.1, part 7: Authentication
draft-ietf-httpbis-p7-auth-02

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Abstract

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.

Editorial Note (To be removed by RFC Editor)

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 http://www.tools.ietf.org/wg/httpbis/trac/report/11 and related documents (including fancy diffs) can be found at http://www.tools.ietf.org/wg/httpbis/.

This draft incorporates those issue resolutions that were either collected in the original RFC2616 errata list (http://purl.org/NET/http-errata), or which were agreed upon on the mailing list between October 2006 and November 2007 (as published in "draft-lafon-rfc2616bis-03").

Table of Contents

1.  Introduction
    1.1.  Requirements
2.  Notational Conventions and Generic Grammar
3.  Status Code Definitions
    3.1.  401 Unauthorized
    3.2.  407 Proxy Authentication Required
4.  Header Field Definitions
    4.1.  Authorization
    4.2.  Proxy-Authenticate
    4.3.  Proxy-Authorization
    4.4.  WWW-Authenticate
5.  IANA Considerations
6.  Security Considerations
    6.1.  Authentication Credentials and Idle Clients
7.  Acknowledgments
8.  References
    8.1.  Normative References
    8.2.  Informative References
Appendix A.  Compatibility with Previous Versions
    A.1.  Changes from RFC 2616
Appendix B.  Change Log (to be removed by RFC Editor before publication)
    B.1.  Since RFC2616
    B.2.  Since draft-ietf-httpbis-p7-auth-00
    B.3.  Since draft-ietf-httpbis-p7-auth-01
§  Index
§  Authors' Addresses
§  Intellectual Property and Copyright Statements

1.  Introduction

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] (Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, “HTTP Authentication: Basic and Digest Access Authentication,” June 1999.), 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] (Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, “HTTP Authentication: Basic and Digest Access Authentication,” June 1999.). This specification adopts the definitions of "challenge" and "credentials" from that specification.

1.1.  Requirements

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] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

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."

2.  Notational Conventions and Generic Grammar

This specification uses the ABNF syntax defined in Section 2.1 of [Part1] (Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., and J. Reschke, Ed., “HTTP/1.1, part 1: URIs, Connections, and Message Parsing,” February 2008.). [abnf.dep] (ABNF syntax and basic rules will be adopted from RFC 5234, see <http://tools.ietf.org/wg/httpbis/trac/ticket/36>.)

The ABNF rules below are defined in other specifications:

  challenge   = <challenge, defined in [RFC2617], Section 1.2>
  credentials = <credentials, defined in [RFC2617], Section 1.2>

3.  Status Code Definitions

3.1.  401 Unauthorized

The request requires user authentication. The response MUST include a WWW-Authenticate header field (Section 4.4 (WWW-Authenticate)) containing a challenge applicable to the requested resource. The client MAY repeat the request with a suitable Authorization header field (Section 4.1 (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 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" [RFC2617] (Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, “HTTP Authentication: Basic and Digest Access Authentication,” June 1999.).

3.2.  407 Proxy Authentication Required

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 4.2 (Proxy-Authenticate)) containing a challenge applicable to the proxy for the requested resource. The client MAY repeat the request with a suitable Proxy-Authorization header field (Section 4.3 (Proxy-Authorization)). HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication" [RFC2617] (Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, “HTTP Authentication: Basic and Digest Access Authentication,” June 1999.).

4.  Header Field Definitions

This section defines the syntax and semantics of HTTP/1.1 header fields related to authentication.

4.1.  Authorization

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 Authorization field value consists of credentials containing the authentication information of the user agent for the realm of the resource being requested.

  Authorization  = "Authorization" ":" credentials

HTTP access authentication is described in "HTTP Authentication: Basic and Digest Access Authentication" [RFC2617] (Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, “HTTP Authentication: Basic and Digest Access Authentication,” June 1999.). 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 Section 9 of [Part6] (Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., and J. Reschke, Ed., “HTTP/1.1, part 6: Caching,” February 2008.)) 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:

1. 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.
2. 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.
3. If the response includes the "public" cache-control directive, it MAY be returned in reply to any subsequent request.

4.2.  Proxy-Authenticate

The Proxy-Authenticate response-header field 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-URI.

  Proxy-Authenticate  = "Proxy-Authenticate" ":" 1#challenge

The HTTP access authentication process is described in "HTTP Authentication: Basic and Digest Access Authentication" [RFC2617] (Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, “HTTP Authentication: Basic and Digest Access Authentication,” June 1999.). 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.

4.3.  Proxy-Authorization

The Proxy-Authorization request-header field 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" ":" credentials

The HTTP access authentication process is described in "HTTP Authentication: Basic and Digest Access Authentication" [RFC2617] (Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, “HTTP Authentication: Basic and Digest Access Authentication,” June 1999.). 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.

4.4.  WWW-Authenticate

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-URI.

  WWW-Authenticate  = "WWW-Authenticate" ":" 1#challenge

The HTTP access authentication process is described in "HTTP Authentication: Basic and Digest Access Authentication" [RFC2617] (Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, “HTTP Authentication: Basic and Digest Access Authentication,” June 1999.). 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.

5.  IANA Considerations

[anchor2] (TBD.)

6.  Security Considerations

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.

6.1.  Authentication Credentials and Idle Clients

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.

7.  Acknowledgments

TBD.

8.  References

8.1. Normative References

8.2. Informative References

Appendix A.  Compatibility with Previous Versions

A.1.  Changes from RFC 2616

Appendix B.  Change Log (to be removed by RFC Editor before publication)

B.1.  Since RFC2616

Extracted relevant partitions from [RFC2616] (Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1,” June 1999.).

B.2.  Since draft-ietf-httpbis-p7-auth-00

Closed issues:

• http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35: "Normative and Informative references"

B.3.  Since draft-ietf-httpbis-p7-auth-01

Ongoing work on ABNF conversion (http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36):

• 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.

Index

Authors' Addresses

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