Internet Engineering Task Force (IETF) J. Reschke

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

Abstract

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.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7615.

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RFC 7615 HTTP Authentication-Info September 2015

Copyright Notice

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
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Without obtaining an adequate license from the person(s) controlling
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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 Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3
3. The Authentication-Info Response Header Field . . . . . . . . 3
3.1. Parameter Value Format . . . . . . . . . . . . . . . . . 4
4. The Proxy-Authentication-Info Response Header Field . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6

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RFC 7615 HTTP Authentication-Info September 2015

1. 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 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.

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 [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.

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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.

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RFC 7615 HTTP Authentication-Info September 2015

6. 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. References

7.1. 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>.

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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: [email protected]
URI: http://greenbytes.de/tech/webdav/

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