Internet Engineering Task Force (IETF) J. Reschke Request for Comments: 7615 greenbytes Obsoletes: 2617 September 2015 Category: Standards Track ISSN: 2070-1721
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 Hypertext Transfer Protocol (HTTP) authentication schemes that need to return information once the client's authentication credentials have been accepted.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.
This specification defines the "Authentication-Info" and "Proxy- Authentication-Info" response header fields for use in HTTP authentication schemes ([RFC7235]) that 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" ([RFC7616]), but also in other future schemes that might have the same requirements for carrying additional information during authentication.
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].
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 [RFC7616].
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 authentication scheme indicated by the Authorization header field ([RFC7235], Section 4.2) of the corresponding request.
A proxy forwarding a response is not allowed to modify the field value in any way.
Reschke Standards Track [Page 3]
RFC 7615 HTTP Authentication-Info September 2015
Authentication-Info can be used inside trailers ([RFC7230], Section 4.1.2) when the authentication scheme explicitly allows this.
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], Section 2) and its semantics are defined by the authentication scheme indicated by the Proxy-Authorization header field ([RFC7235], Section 4.4) of the corresponding request:
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.
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.
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.