HTTP Authentication-Info and
Proxy&nbhy;Authentication&nbhy;Info Response Header Fieldsgreenbytes GmbHHafenweg 16MuensterNW48155Germanyjulian.reschke@greenbytes.dehttp://greenbytes.de/tech/webdav/
Applications
HTTP Working GroupHTTPauthentication
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.
This specification defines the "Authentication-Info" and
"Proxy-Authentication-Info" response header fields for use in HTTP authentication
schemes () that need to return
information once the client's authentication credentials have been accepted.
Both were previously defined in Section 3 of , defining
the HTTP "Digest" authentication scheme. This document generalizes
the description for use not only in "Digest" (), 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
with a list extension, defined in
Section 7 of , 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 .
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 .
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 .
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
(, Section 4.2)
of the corresponding request.
A proxy forwarding a response is not allowed to modify the field value in any
way.
Authentication-Info can be used inside trailers
(, 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 ).
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.
The Proxy-Authentication-Info response header field is equivalent to
Authentication-Info, except that it applies to proxy authentication
(, Section 2) and its semantics are defined by the
authentication scheme indicated by the Proxy-Authorization header
field (, Section 4.4) of the corresponding request:
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.
HTTP header fields are registered within the "Message Headers" registry
located at ,
as defined by .
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 NameProtocolStatusReferenceAuthentication-Infohttpstandard of this document
Proxy-Authentication-Infohttpstandard of this document
Registration Procedures for Message Header FieldsThis specification defines registration procedures for the message header fields used by Internet mail, HTTP, Netnews and other applications. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.HTTP Digest Access Authentication
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.