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 additional information during or after authentication.¶

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This specification defines the "Authentication-Info" and "Proxy-Authentication-Info" response header fields for use in HTTP authentication schemes ([RFC7235]) which need to return additional information during or after authentication.¶

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 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 additional information regarding the successful 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].¶

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. Intermediaries are not allowed to modify the field value in any way. Authentication-Info can be used inside trailers ([RFC7230], Section 4.1.2).¶

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 <http://www.iana.org/assignments/message-headers>, as defined by [BCP90].¶

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, Yutaka Oiwa, Rifaat Shekh-Yusef, and Martin Thomson.¶