HTTPbis Working GroupJ. Reschke
Updates: 2617 (if approved)March 3, 2015
Intended status: Standards Track
Expires: September 4, 2015

The Hypertext Transfer Protocol (HTTP) Authentication-Info and Proxy-Authentication-Info Response Header Fields


This specification defines the "Authentication-Info" and "Proxy-Authentication-Info" response header fields for use in HTTP authentication schemes which need to return information once the client's authentication credentials have been accepted.

Editorial Note (To be removed by RFC Editor)

Discussion of this draft takes place on the HTTPBIS working group mailing list (, which is archived at <>.

Working Group information can be found at <> and <>; source code and issues list for this draft can be found at <>.

The changes in this draft are summarized in Appendix A.4.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on September 4, 2015.

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1. Introduction

This specification defines the "Authentication-Info" and "Proxy-Authentication-Info" response header fields for use in HTTP authentication schemes ([RFC7235]) which need to return information once the client's authentication credentials have been accepted.

Both were previously defined in Section 3 of [RFC2617], defining the HTTP "Digest" authentication scheme. This document generalizes the description for use not only in "Digest" ([DIGEST]), but also in other future schemes that might have the same requirements for carrying additional information during authentication.

2. Notational Conventions

This specification uses the Augmented Backus-Naur Form (ABNF) notation of [RFC5234] with a list extension, defined in Section 7 of [RFC7230], that allows for compact definition of comma-separated lists using a '#' operator (similar to how the '*' operator indicates repetition). The ABNF production for "auth-param" is defined in Section 2.1 of [RFC7235].

3. The Authentication-Info Response Header Field

HTTP authentication schemes can use the Authentication-Info response header field to communicate information after the client's authentication credentials have been accepted. This information can include a finalization message from the server (e.g., it can contain the server authentication).

The field value is a list of parameters (name/value pairs), using the "auth-param" syntax defined in Section 2.1 of [RFC7235]. This specification only describes the generic format; authentication schemes using "Authentication-Info" will define the individual parameters. The "Digest" Authentication Scheme, for instance, defines multiple parameters in Section 3.5 of [DIGEST].

  Authentication-Info = #auth-param

The Authentication-Info header field can be used in any HTTP response, independently of request method and status code. Its semantics are defined by the applicable authentication scheme.

A proxy forwarding a response is not allowed to modify the field value in any way.

Authentication-Info can be used inside trailers ([RFC7230], Section 4.1.2) when the authentication scheme explicitly allows this.

3.1. Parameter Value Format

Parameter values can be expressed either as "token" or as "quoted-string" (Section 3.2.6 of [RFC7230]).

Authentication scheme definitions need to allow both notations, both for senders and recipients. This allows recipients to use generic parsing components, independent of the authentication scheme in use.

For backwards compatibility, authentication scheme definitions can restrict the format for senders to one of the two variants. This can be important when it is known that deployed implementations will fail when encountering one of the two formats.

4. The Proxy-Authentication-Info Response Header Field

The Proxy-Authentication-Info response header field is equivalent to Authentication-Info, except that it applies to proxy authentication ([RFC7235]):

  Proxy-Authentication-Info = #auth-param

However, unlike Authentication-Info, the Proxy-Authentication-Info header field applies only to the next outbound client on the response chain. This is because only the client that chose a given proxy is likely to have the credentials necessary for authentication. However, when multiple proxies are used within the same administrative domain, such as office and regional caching proxies within a large corporate network, it is common for credentials to be generated by the user agent and passed through the hierarchy until consumed. Hence, in such a configuration, it will appear as if Proxy-Authentication-Info is being forwarded because each proxy will send the same field value.

5. Security Considerations

Adding information to HTTP responses that are sent over an unencrypted channel can affect security and privacy. The presence of the header fields alone indicates that HTTP authentication is in use. Additional information could be exposed by the contents of the authentication-scheme specific parameters; this will have to be considered in the definitions of these schemes.

6. IANA Considerations

HTTP header fields are registered within the "Message Headers" registry located at <>, as defined by [BCP90].

This document updates the definitions of the "Authentication-Info" and "Proxy-Authentication-Info" header fields, so the "Permanent Message Header Field Names" registry shall be updated accordingly:

Header Field NameProtocolStatusReference
Authentication-InfohttpstandardSection 3 of this document
Proxy-Authentication-InfohttpstandardSection 4 of this document

7. Acknowledgements

This document is based on the header field definitions in RFCs 2069 and 2617, whose authors are: John Franks, Phillip M. Hallam-Baker, Jeffery L. Hostetler, Scott D. Lawrence, Paul J. Leach, Ari Luotonen, Eric W. Sink, and Lawrence C. Stewart.

Additional thanks go to the members of the HTTPAuth and HTTPbis Working Groups, namely Amos Jeffries, Benjamin Kaduk, Alexey Melnikov, Mark Nottingham, Yutaka Oiwa, Rifaat Shekh-Yusef, and Martin Thomson.

8. References

8.1. Normative References

Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF”, STD 68, RFC 5234, January 2008, <>.
Fielding, R., Ed. and J. Reschke, Ed., “Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing”, RFC 7230, June 2014, <>.
Fielding, R., Ed. and J. Reschke, Ed., “Hypertext Transfer Protocol (HTTP/1.1): Authentication”, RFC 7235, June 2014, <>.

8.2. Informative References

Klyne, G., Nottingham, M., and J. Mogul, “Registration Procedures for Message Header Fields”, BCP 90, RFC 3864, September 2004, <>.
Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, “HTTP Digest Access Authentication”, Internet-Draft draft-ietf-httpauth-digest-14 (work in progress), February 2015.
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, <>.

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

A.1. draft-reschke-httpauth-auth-info-00

Changed boilerplate to make this an HTTPbis WG draft. Added Acknowledgements.

In the Security Considerations, remind people that those apply to unencryped channels.

Make it clearer that these are really just response header fields.

A.2. draft-ietf-httpbis-auth-info-00

Rephrase introduction of header field to be closer to what RFC 2617 said ("successful authentication").

Update DIGEST reference.

A.3. draft-ietf-httpbis-auth-info-01

State that scheme definitions need to define whether the header field can be used in trailers.

Add "updates: 2617" to boilerplate.

A.4. draft-ietf-httpbis-auth-info-02

Updated DIGEST reference.

Clarify purpose of header consistently (<>).

The do-not-modify rule does not include proxies that consume Authentication-Info (<>).

Borrow more proxy auth related considerations from RFC 7235 for the description of Proxy-Authentication-Info (<>).

Author's Address

Julian F. Reschke
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155