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Network Working Group                                        R. Van Rein
Internet-Draft                                          InternetWide.org
Intended status: Standards Track                        January 31, 2020
Expires: August 3, 2020

                     HTTP Resources with User Names


   Many protocols support users under domain names, but HTTP does not.
   Usage patterns in the wild do suggest a desire to have this facility.
   This specification defines a header for user names, orthogonal to
   authenticated identities.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 3, 2020.

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   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  The HTTP User Header  . . . . . . . . . . . . . . . . . . . .   3
   3.  URI with User Information . . . . . . . . . . . . . . . . . .   3
   4.  Protocol Handling of URI and User . . . . . . . . . . . . . .   4
   5.  Environment Variable with Local User  . . . . . . . . . . . .   5
   6.  Orthogonality of Authentication (Example) . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Compatibility with Basic Authentication  . . . . . .   8
   Appendix B.  Compatibility with RESTful Patterns  . . . . . . . .   9
   Appendix C.  Compatibility with Caching . . . . . . . . . . . . .  10
   Appendix D.  Acknowledgements . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Many protocols support global identities like john@example.com to
   identify users like john under domains such as example.com.  The URI
   format for HTTP can express [Section 2.7.1 of [RFC7230]] such
   authority components, with an intended interpretation of locating a
   user-specific resources.  Many online applications publish about
   individual users, but there is no standard in HTTP to express user
   names to address them.  This specification therefore introduces a
   header "User", in close parallel to the "Host" header.

   Some current URIs for HTTP have used the userinfo field in the URI to
   express an authentication user, in spite of the intended use to
   refine the authority information.  This conflates the user part of
   the resource with the (authenticated) client-side identity.  This
   specification makes authentication and resource user two orthogonal
   concepts, and specifies a clear relation to the URI format.

   Orthogonality yields a generalisation, but voluntary conflation of
   the user concepts remains possible, and may even be useful as default
   behaviour.  Servers can be configured with resource users that demand
   authentication with the same client name; they may even accept
   authentication as a bypass to a resource user.  Clients may accept
   authentication requests and use their submitted resource user as a
   hint to the authentication user.

   Orthogonal concepts can however be untied to support advanced use
   cases, of which these practices are a specific form.  Servers may
   welcome members to authenticate against a shared/group resource.

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   Clients treat the resource user as part of the realm identity and can
   use it to locate the customary authentication user for that realm.
   Credentials need not be tied to the server, so it is possible to
   "bring your own identity" by facilitating realm crossover for

   The purpose of this specification is to define clear meaning for HTTP
   URIs with a userinfo component and their mapping to HTTP.

2.  The HTTP User Header

   The "User" header field provides an aspect of the desired resource
   name scope.  The value can be inserted by software or be taken from
   the visible portion of the userinfo component [Section 3.2 of
   [RFC3986]] of the target URI but it MUST NOT include a ":" colon
   (U+003a) character.

   The User header value holds precisely one value with the following
   ABNF grammar:

   User = *( unreserved / pct-encoded / sub-delims )

   The referenced non-terminals are as for URIs [RFC3986] and can be
   directly included in the quoted-string header form; a plain token
   cannot express "(", ")", "=", ";" and "," without escaping
   [Section 3.2.6 of [RFC7230]].

3.  URI with User Information

   This section is informative.

   The use of a user name in the authority component of a URI is a
   general concept, already used for addressing users with SMTP, SIP,
   XMPP and many other protocols.  By allowing users in HTTP resource
   names, better crossover of identities with these protocols can be
   achieved.  Unlike server-specific user name mapping conventions, the
   specified generic meaning of URI userinfo as part of the authority
   information enables such crossovers to be automated.

   There is a current practice of writing an authentication name in the
   userinfo portion of a URI.  This can be useful if it adds Basic
   authentication to the first request; Basic can do this because it
   does not incorporate a server-sent challenge.

   Having never been standardised, the mechanistic side of this practice
   is highly diverse, and URIs are far from portable between browsers or
   even the various places where they occur within one browser.  As a
   result, these URIs cannot be spread freely and their usage pattern is

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   dedicated to the client software in use.  On grounds of this
   immobility, it would have been sufficient to not break this practice.
   What this specification does is completely support [Appendix A] this
   pattern as a special case.

   This specification follows the URI's intention of the userinfo field,
   and prescribes copying its value into the User header.  It will
   however remove anything from a colon onward, to suppress the portion
   of userinfo that is prescribed to not be rendered.

   Both the general userinfo format and the removal of anything starting
   from a colon may lead to an empty string as the User header value.
   Servers may interpret this empty User header as they see fit; the
   underlying resource may be a default page, for example one that asks
   for a user name to redirect to.  After client authentication, such a
   page may list user names that would be accessible.

4.  Protocol Handling of URI and User

   User agents are supposed to render userinfo in the target URI (up to
   the first colon ":" (U+003a) if it contains any [Section 3.2.1 of
   [RFC3986]]) where it may be helpful if it stands out graphically
   [Section 7.6 of [RFC3986]].  User agents SHOULD NOT remove userinfo
   from the target URI.

   Compliant user agents MUST pass userinfo in the target URI (up to the
   first colon ":" (U+003a) if it contains any) as a User header field
   if, and only if, the target URI contains a userinfo part.

   The User header MAY appear in requests and MUST NOT occur in

   When sending it, the user agent SHOULD generate User as the next
   header field after Host.  Transparent intermediates such as proxies
   and caches MUST NOT add, remove or modify the User header.  The
   CONNECT method and Host header both exclude this information, so the
   User header complements them.

   Compliant servers MAY ignore the User header [Section 3.2.1 of
   [RFC7230]] and they MAY impose a more restrictive grammar (like a
   NAI's utf8-username [RFC7542]) than the URI syntax before further
   processing it.  When they do use it, the Effective Request URI
   [Section 5.5 of [RFC7230]] MUST be constructed with the userinfo and
   the "@" at delimiter (U+0040) prefixed to the host name and optional
   port.  Realms are specific to an authority section [Section 2.2 of
   [RFC7235]] and so a realm never spans across different userinfo

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   As a result of a consistent translation of any User header value into
   the Effective Request URI, the server would map consistently to
   resources.  It is merely enabled to include a User header as an extra
   input variable to this mapping to resources.

   HTTP caches [RFC7234] derive no privacy or security concerns from the
   User header, but they do need to differentiate requests based on it.
   To accommodate that, the Vary header [Section 7.1.4 of [RFC7231]]
   MUST be generated by the server in the matching response, and the
   header MUST either be a single "*" star (U+002a) or list the "User"
   name, for all responses whose processing was influenced by the User
   header.  This requirement has no bearing on software and
   configurations that ignore the User header.

   During redirects or other traversals to relative HTTP URIs, compliant
   user agents MUST overwrite the userinfo in the target URI when the
   new URI specifies an authority component, and MUST keep it otherwise.

5.  Environment Variable with Local User

   The following variable SHOULD be passed to applications that run on
   top of the HTTP stack in a server:

   LOCAL_USER  gives the HTTP User header value after syntax checking
         and percent-decoding.  Like the customary variables HTTP_HOST
         and PATH_INFO, this specifies the resource being requested.
         The HTTP_USER header does not describe the identity of the
         client-side user, which usually lands in a variable REMOTE_USER
         after authentication.

6.  Orthogonality of Authentication (Example)

   This section is informative.

   The authority user in a URI refines the server's resource name space,
   and the server is free to distinguish this resource user from an
   authenticated client identity.  The example below demonstrates the
   expressive power gained by treating these user concepts as separate,
   in an advanced pattern of use in which an individual user accesses a
   group resource.  This advanced binding between the group resource and
   an authenticated client can build on access control lists.

   John and Mary both work at the Sales department of Example, Inc and
   John has written a document that he wants Mary to review.  Mary opens
   a link to the document name space under the shared sales account at
   https://sales@example.com/docs and her user agent sends:

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   GET /docs HTTP/1.1
   Host: example.com
   User: sales

   The server redirects to add a slash, and when this is specific to the
   sales name space, it must inform caches about this with the Vary

   HTTP/1.1 301 Moved Permanently
   Location: /docs/
   Vary: User

   Since the new location lacks an authority component, this part is
   retained from the referring URI, and the user agent redirects to
   https://sales@example.com/docs/ by sending:

   GET /docs/ HTTP/1.1
   Host: example.com
   User: sales

   By this time, the server runs into access control, and decides that
   it needs an authenticated user identity.  To this end, it responds
   with a challenge to the "Documents" realm:

   HTTP/1.1 401 Unauthorized
   WWW-Authenticate: KnockKnock realm="Documents"
   Vary: User

   Mary's user agent needs to collect credentials, and may hint at the
   user name "sales" from the URI but, this being the name of a shared
   resource, Mary has no fitting credentials and instead authenticates
   as "mary":

   GET /docs/ HTTP/1.1
   Host: example.com
   User: sales
   Authorization: KnockKnock realm="Documents", user="mary", ...

   At some point, the server accepts Mary's authentication and proceeds
   to access control.  This phase checks if user "mary" may access realm
   "Documents" of "https://sales@example.com" by checking that Mary
   works for the Sales department.  Once this is assured, the server
   returns the requested document list:

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   HTTP/1.1 200 OK
   Vary: User
   Content-Type: text/html

   <a href="/docs/review.cgi?docid=123">Review 123 now</a>

   Mary clicks on the link to /docs/review.cgi?docid=123 and her user
   agent sees a relative reference with no authority component, so this
   is again reused from the referring URI.  The new URI is
   https://sales@example.com/docs/review.cgi?docid=123 with same root
   https://sales@example.com for which Mary has established credentials,
   so the same realm can be tried.  The user agent therefore sends:

   GET /docs/review.cgi?docid=123 HTTP/1.1
   Host: example.com
   User: sales
   Authorization: KnockKnock realm="Documents", user="mary", ...

   After access control, the server starts the CGI script with
   environment variables LOCAL_USER=sales and REMOTE_USER=mary of which
   only the latter is an authenticated result.  The script interprets
   the LOCAL_USER as a group account and the REMOTE_USER as the acting
   group member, and returns a page for review of the document and Mary
   can get to work.

7.  IANA Considerations

   IANA adds the following entry to the Message Headers registry:

   Header Field Name   Template   Protocol   Status    Reference
   ------------------  ---------  ---------  -------   ----------
   User                           http       TBD       TBD:THIS_SPEC

8.  Security Considerations

   The User header field as defined herein is orthogonal to issues of
   authentication and authorisation, and adds no security concerns.

9.  References

9.1.  Normative References

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,

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   [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,

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,

   [RFC7234]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
              RFC 7234, DOI 10.17487/RFC7234, June 2014,

   [RFC7235]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Authentication", RFC 7235,
              DOI 10.17487/RFC7235, June 2014,

9.2.  Informative References

   [RFC7542]  DeKok, A., "The Network Access Identifier", RFC 7542,
              DOI 10.17487/RFC7542, May 2015,

Appendix A.  Compatibility with Basic Authentication

   This appendix is informative.

   Basic authentication is regularly used as a quick and easy HTTP
   authentication technique.  Several user agents continue to support it
   with the "user:password@" URI prefix to a hostname, despite its
   deprecation [Section 3.2.1 of [RFC3986]].  This specification imposes
   no new constraints on this practice; it merely prescribes to send the
   User header field, and leaves it to client software whether it also
   sends Basic authentication.

   The mapping from authority names to resources is the prerogative of
   the server.  A server supportive of resource selection through Basic
   authentication could ignore the User header field and still comply
   with this specification.  A server that does recognise the User
   header field would use it to locate a resource, before deciding about
   access control to that resource; it may subsequently require
   authentication, and select schemes that could be supported.  At this
   time, it may or may not welcome an added Basic authentication
   attempt.  All this depends on server configuration.

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   This flexibility can support a transition from Basic authentication
   to User headers on the server, and allows client software to also
   migrate by first adding the User header, and later supporting the
   advanced uses by allowing differentiation between resource user and
   authentication user.  Server administrators have a free choice
   whether to gradually phase out older clients or to continue to
   support them.

   Sending both the User header and Basic authentication is only to be
   expected from user agents who conflate authority userinfo with
   authentication user.  Such user agents will be less flexible, and
   will not be able to support more advanced usage patterns that
   separate these concepts, such as shared/group resources addressed
   with the User header field and, when desired, authentication through
   an independent set of headers.  Among the tools to drive separate
   authentication could be the negotiation of more advanced mechanisms,
   even just Digest authentication.

Appendix B.  Compatibility with RESTful Patterns

   This appendix is informative.

   Whether and how the User header is interpreted is the prerogative of
   the server.  The server will translate resources in the same manner
   when provided with the same User header, and may do so without regard
   for the method used.  The main concern is now if it will be addressed
   in the same manner in every case.  This depends on the user agents.

   Development environments make sending the User header field simple,
   so application support is as easy as the applications are flexible.
   Binary user agents and ones that may lag behind in updates do however
   call for backward compatibility support of consistent translation to

   Backward compatibility can be guaranteed for host names that always
   require a User header; such resources may be described with a URI
   holding a (possibly empty) userinfo field.  Failure to send a User
   header to such resources when the URI holds one can be assumed to
   have originated from a user agent that fails to support it.  When an
   offer for Basic authentication is presented, it may be interpreted as
   the conflated approach to userinfo, and treated as a substitute for
   the User header.  If neither is offered, then an error may be
   reported or control redirected to another means of selecting a
   resource user, perhaps through an alternate local naming convention.

   This indicates that the server is able to detect inconsistent
   tranlation risks, and avoid accidentally binding a request to an
   unintended resource as a result of a missing User header.

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Appendix C.  Compatibility with Caching

   This appendix is informative.

   Whether and how the User header is used to find resources is the
   prerogative of their server.  A conservative cache design might
   insert the User header value in request URIs, but lose the capability
   of seeing the equivalence of a resource as perceived by the server.
   The inclusion of the name "User" in the Vary header of the response
   adds explicit non-equivalence information, and thereby provides a
   more accurate cache controlling instruction.

   Whether a result is "private" is independent of the User header, as
   that only signifies a refinement of the resource name space on the
   server.  The rules that signify authentication as default indicator
   of privacy is orthogonal to the User header.  Independent inclusion
   of Basic authentication may still invalidate caching, but not as a
   result of this specification.

Appendix D.  Acknowledgements

   This specification could be improved thanks to input from Daniel
   Stenberg, Amos Jeffries, Paul Vixie, James Fuller and Henri Manson.

Author's Address

   Rick van Rein
   Haarlebrink 5
   Enschede, Overijssel  7544 WP
   The Netherlands

   Email: rick@openfortress.nl

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