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Internet Engineering Task Force (IETF)                        J. ReschkeRequest for Comments: 7615                                    greenbytesObsoletes:2617                                           September 2015Category: Standards TrackISSN: 2070-1721HTTP Authentication-Info and Proxy-Authentication-InfoResponse Header FieldsAbstract   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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7615.Reschke                      Standards Track                    [Page 1]

RFC 7615                HTTP Authentication-Info          September 2015Copyright Notice   Copyright (c) 2015 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .32.  Notational Conventions  . . . . . . . . . . . . . . . . . . .33.  The Authentication-Info Response Header Field . . . . . . . .33.1.  Parameter Value Format  . . . . . . . . . . . . . . . . .44.  The Proxy-Authentication-Info Response Header Field . . . . .45.  Security Considerations . . . . . . . . . . . . . . . . . . .46.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .57.  References  . . . . . . . . . . . . . . . . . . . . . . . . .57.1.  Normative References  . . . . . . . . . . . . . . . . . .57.2.  Informative References  . . . . . . . . . . . . . . . . .5   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .6   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .6Reschke                      Standards Track                    [Page 2]

RFC 7615                HTTP Authentication-Info          September 20151.  Introduction   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 inSection 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.2.  Notational Conventions   This specification uses the Augmented Backus-Naur Form (ABNF)   notation of [RFC5234] with a list extension, defined inSection 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 inSection 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 inSection 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 inSection 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.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], 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.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.Reschke                      Standards Track                    [Page 4]

RFC 7615                HTTP Authentication-Info          September 20156.  IANA Considerations   HTTP header fields are registered within the "Message Headers"   registry located at <http://www.iana.org/assignments/message-headers>, 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 has been updated accordingly:   +---------------------------+----------+----------+-----------------+   | Header Field Name         | Protocol | Status   | Reference       |   +---------------------------+----------+----------+-----------------+   | Authentication-Info       | http     | standard |Section 3 of    |   |                           |          |          | this document   |   | Proxy-Authentication-Info | http     | standard |Section 4 of    |   |                           |          |          | this document   |   +---------------------------+----------+----------+-----------------+7.  References7.1.  Normative References   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax              Specifications: ABNF", STD 68,RFC 5234,              DOI 10.17487/RFC5234, January 2008,              <http://www.rfc-editor.org/info/rfc5234>.   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer              Protocol (HTTP/1.1): Message Syntax and Routing",RFC 7230, DOI 10.17487/RFC7230, June 2014,              <http://www.rfc-editor.org/info/rfc7230>.   [RFC7235]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer              Protocol (HTTP/1.1): Authentication",RFC 7235,              DOI 10.17487/RFC7235, June 2014,              <http://www.rfc-editor.org/info/rfc7235>.7.2.  Informative References   [BCP90]    Klyne, G., Nottingham, M., and J. Mogul, "Registration              Procedures for Message Header Fields",BCP 90,RFC 3864,              September 2004, <http://www.rfc-editor.org/info/bcp90>.Reschke                      Standards Track                    [Page 5]

RFC 7615                HTTP Authentication-Info          September 2015   [RFC2617]  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, DOI 10.17487/RFC2617, June 1999,              <http://www.rfc-editor.org/info/rfc2617>.   [RFC7616]  Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP              Digest Access Authentication",RFC 7616,              DOI 10.17487/RFC7616, September 2015,              <http://www.rfc-editor.org/info/rfc7616>.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.Author's Address   Julian F. Reschke   greenbytes GmbH   Hafenweg 16   Muenster, NW  48155   Germany   Email: julian.reschke@greenbytes.de   URI:http://greenbytes.de/tech/webdav/Reschke                      Standards Track                    [Page 6]