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HTTPbis Working Group                                   R. Fielding, Ed.
Internet-Draft                                                     Adobe
Obsoletes: 2616 (if approved)                            J. Reschke, Ed.
Updates: 2617 (if approved)                                   greenbytes
Intended status: Standards Track                       November 17, 2013
Expires: May 21, 2014


         Hypertext Transfer Protocol (HTTP/1.1): Authentication
                     draft-ietf-httpbis-p7-auth-25

Abstract

   The Hypertext Transfer Protocol (HTTP) is an application-level
   protocol for distributed, collaborative, hypermedia information
   systems.  This document defines the HTTP Authentication framework.

Editorial Note (To be removed by RFC Editor)

   Discussion of this draft takes place on the HTTPBIS working group
   mailing list (ietf-http-wg@w3.org), which is archived at
   <http://lists.w3.org/Archives/Public/ietf-http-wg/>.

   The current issues list is at
   <http://tools.ietf.org/wg/httpbis/trac/report/3> and related
   documents (including fancy diffs) can be found at
   <http://tools.ietf.org/wg/httpbis/>.

   The changes in this draft are summarized in Appendix D.1.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 21, 2014.

Copyright Notice



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   Copyright (c) 2013 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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   This document may contain material from IETF Documents or IETF
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   it for publication as an RFC or to translate it into languages other
   than English.



























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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Conformance and Error Handling . . . . . . . . . . . . . .  4
     1.2.  Syntax Notation  . . . . . . . . . . . . . . . . . . . . .  4
   2.  Access Authentication Framework  . . . . . . . . . . . . . . .  4
     2.1.  Challenge and Response . . . . . . . . . . . . . . . . . .  4
     2.2.  Protection Space (Realm) . . . . . . . . . . . . . . . . .  6
   3.  Status Code Definitions  . . . . . . . . . . . . . . . . . . .  7
     3.1.  401 Unauthorized . . . . . . . . . . . . . . . . . . . . .  7
     3.2.  407 Proxy Authentication Required  . . . . . . . . . . . .  7
   4.  Header Field Definitions . . . . . . . . . . . . . . . . . . .  7
     4.1.  Authorization  . . . . . . . . . . . . . . . . . . . . . .  7
     4.2.  Proxy-Authenticate . . . . . . . . . . . . . . . . . . . .  8
     4.3.  Proxy-Authorization  . . . . . . . . . . . . . . . . . . .  8
     4.4.  WWW-Authenticate . . . . . . . . . . . . . . . . . . . . .  9
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
     5.1.  Authentication Scheme Registry . . . . . . . . . . . . . . 10
       5.1.1.  Procedure  . . . . . . . . . . . . . . . . . . . . . . 10
       5.1.2.  Considerations for New Authentication Schemes  . . . . 10
     5.2.  Status Code Registration . . . . . . . . . . . . . . . . . 11
     5.3.  Header Field Registration  . . . . . . . . . . . . . . . . 12
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
     6.1.  Authentication Credentials and Idle Clients  . . . . . . . 12
     6.2.  Protection Spaces  . . . . . . . . . . . . . . . . . . . . 13
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Appendix A.  Changes from RFCs 2616 and 2617 . . . . . . . . . . . 15
   Appendix B.  Imported ABNF . . . . . . . . . . . . . . . . . . . . 15
   Appendix C.  Collected ABNF  . . . . . . . . . . . . . . . . . . . 15
   Appendix D.  Change Log (to be removed by RFC Editor before
                publication)  . . . . . . . . . . . . . . . . . . . . 16
     D.1.  Since draft-ietf-httpbis-p7-auth-24  . . . . . . . . . . . 16
   Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17















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1.  Introduction

   This document defines HTTP/1.1 access control and authentication.  It
   includes the relevant parts of RFC 2616 with only minor changes
   ([RFC2616]), plus the general framework for HTTP authentication, as
   previously defined in "HTTP Authentication: Basic and Digest Access
   Authentication" ([RFC2617]).

   HTTP provides several OPTIONAL challenge-response authentication
   schemes that can be used by a server to challenge a client request
   and by a client to provide authentication information.  The "basic"
   and "digest" authentication schemes continue to be specified in RFC
   2617.

1.1.  Conformance and Error Handling

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Conformance criteria and considerations regarding error handling are
   defined in Section 2.5 of [Part1].

1.2.  Syntax Notation

   This specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234] with the list rule extension defined in Section
   7 of [Part1].  Appendix B describes rules imported from other
   documents.  Appendix C shows the collected ABNF with the list rule
   expanded.

2.  Access Authentication Framework

2.1.  Challenge and Response

   HTTP provides a simple challenge-response authentication framework
   that can be used by a server to challenge a client request and by a
   client to provide authentication information.  It uses a case-
   insensitive token as a means to identify the authentication scheme,
   followed by additional information necessary for achieving
   authentication via that scheme.  The latter can either be a comma-
   separated list of parameters or a single sequence of characters
   capable of holding base64-encoded information.

   Parameters are name-value pairs where the name is matched case-
   insensitively, and each parameter name MUST only occur once per
   challenge.




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     auth-scheme    = token

     auth-param     = token BWS "=" BWS ( token / quoted-string )

     token68        = 1*( ALPHA / DIGIT /
                          "-" / "." / "_" / "~" / "+" / "/" ) *"="

   The "token68" syntax allows the 66 unreserved URI characters
   ([RFC3986]), plus a few others, so that it can hold a base64,
   base64url (URL and filename safe alphabet), base32, or base16 (hex)
   encoding, with or without padding, but excluding whitespace
   ([RFC4648]).

   The 401 (Unauthorized) response message is used by an origin server
   to challenge the authorization of a user agent.  This response MUST
   include a WWW-Authenticate header field containing at least one
   challenge applicable to the requested resource.

   The 407 (Proxy Authentication Required) response message is used by a
   proxy to challenge the authorization of a client and MUST include a
   Proxy-Authenticate header field containing at least one challenge
   applicable to the proxy for the requested resource.

     challenge   = auth-scheme [ 1*SP ( token68 / #auth-param ) ]

      Note: Many clients fail to parse challenges containing unknown
      schemes.  A workaround for this problem is to list well-supported
      schemes (such as "basic") first.

   A user agent that wishes to authenticate itself with an origin server
   -- usually, but not necessarily, after receiving a 401 (Unauthorized)
   -- can do so by including an Authorization header field with the
   request.

   A client that wishes to authenticate itself with a proxy -- usually,
   but not necessarily, after receiving a 407 (Proxy Authentication
   Required) -- can do so by including a Proxy-Authorization header
   field with the request.

   Both the Authorization field value and the Proxy-Authorization field
   value contain the client's credentials for the realm of the resource
   being requested, based upon a challenge received in a response
   (possibly at some point in the past).  When creating their values,
   the user agent ought to do so by selecting the challenge with what it
   considers to be the most secure auth-scheme that it understands,
   obtaining credentials from the user as appropriate.

     credentials = auth-scheme [ 1*SP ( token68 / #auth-param ) ]



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   Upon receipt of a request for a protected resource that omits
   credentials, contains invalid credentials (e.g., a bad password) or
   partial credentials (e.g., when the authentication scheme requires
   more than one round trip), an origin server SHOULD send a 401
   (Unauthorized) response that contains a WWW-Authenticate header field
   with at least one (possibly new) challenge applicable to the
   requested resource.

   Likewise, upon receipt of a request that requires authentication by
   proxies that omit credentials or contain invalid or partial
   credentials, a proxy SHOULD send a 407 (Proxy Authentication
   Required) response that contains a Proxy-Authenticate header field
   with a (possibly new) challenge applicable to the proxy.

   A server receiving credentials that are valid, but not adequate to
   gain access, ought to respond with the 403 (Forbidden) status code
   (Section 6.5.3 of [Part2]).

   HTTP does not restrict applications to this simple challenge-response
   framework for access authentication.  Additional mechanisms can be
   used, such as authentication at the transport level or via message
   encapsulation, and with additional header fields specifying
   authentication information.  However, such additional mechanisms are
   not defined by this specification.

   A proxy MUST forward the WWW-Authenticate and Authorization header
   fields unmodified and follow the rules found in Section 4.1.

2.2.  Protection Space (Realm)

   The authentication parameter realm is reserved for use by
   authentication schemes that wish to indicate the scope of protection.

   A protection space is defined by the canonical root URI (the scheme
   and authority components of the effective request URI; see Section
   5.5 of [Part1]) of the server being accessed, in combination with the
   realm value if present.  These realms allow the protected resources
   on a server to be partitioned into a set of protection spaces, each
   with its own authentication scheme and/or authorization database.
   The realm value is a string, generally assigned by the origin server,
   which can have additional semantics specific to the authentication
   scheme.  Note that a response can have multiple challenges with the
   same auth-scheme but different realms.

   The protection space determines the domain over which credentials can
   be automatically applied.  If a prior request has been authorized,
   the user agent MAY reuse the same credentials for all other requests
   within that protection space for a period of time determined by the



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   authentication scheme, parameters, and/or user preferences (such as a
   configurable inactivity timeout).  Unless specifically allowed by the
   authentication scheme, a single protection space cannot extend
   outside the scope of its server.

   For historical reasons, a sender MUST only generate the quoted-string
   syntax.  Recipients might have to support both token and quoted-
   string syntax for maximum interoperability with existing clients that
   have been accepting both notations for a long time.

3.  Status Code Definitions

3.1.  401 Unauthorized

   The 401 (Unauthorized) status code indicates that the request has not
   been applied because it lacks valid authentication credentials for
   the target resource.  The origin server MUST send a WWW-Authenticate
   header field (Section 4.4) containing at least one challenge
   applicable to the target resource.  If the request included
   authentication credentials, then the 401 response indicates that
   authorization has been refused for those credentials.  The user agent
   MAY repeat the request with a new or replaced Authorization header
   field (Section 4.1).  If the 401 response contains the same challenge
   as the prior response, and the user agent has already attempted
   authentication at least once, then the user agent SHOULD present the
   enclosed representation to the user, since it usually contains
   relevant diagnostic information.

3.2.  407 Proxy Authentication Required

   The 407 (Proxy Authentication Required) status code is similar to 401
   (Unauthorized), but indicates that the client needs to authenticate
   itself in order to use a proxy.  The proxy MUST send a Proxy-
   Authenticate header field (Section 4.2) containing a challenge
   applicable to that proxy for the target resource.  The client MAY
   repeat the request with a new or replaced Proxy-Authorization header
   field (Section 4.3).

4.  Header Field Definitions

   This section defines the syntax and semantics of HTTP/1.1 header
   fields related to authentication.

4.1.  Authorization

   The "Authorization" header field allows a user agent to authenticate
   itself with an origin server -- usually, but not necessarily, after
   receiving a 401 (Unauthorized) response.  Its value consists of



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   credentials containing the authentication information of the user
   agent for the realm of the resource being requested.

     Authorization = credentials

   If a request is authenticated and a realm specified, the same
   credentials are presumed to be valid for all other requests within
   this realm (assuming that the authentication scheme itself does not
   require otherwise, such as credentials that vary according to a
   challenge value or using synchronized clocks).

   See Section 3.2 of [Part6] for details of and requirements pertaining
   to handling of the Authorization field by HTTP caches.

4.2.  Proxy-Authenticate

   The "Proxy-Authenticate" header field consists of at least one
   challenge that indicates the authentication scheme(s) and parameters
   applicable to the proxy for this effective request URI (Section 5.5
   of [Part1]).  It MUST be included as part of a 407 (Proxy
   Authentication Required) response.

     Proxy-Authenticate = 1#challenge

   Unlike WWW-Authenticate, the Proxy-Authenticate header field applies
   only to the next outbound client on the response chain that chose to
   direct its request to the responding proxy.  If that recipient is
   also a proxy, it will generally consume the Proxy-Authenticate header
   field (and generate an appropriate Proxy-Authorization in a
   subsequent request) rather than forward the header field to its own
   outbound clients.  However, if a recipient proxy needs to obtain its
   own credentials by requesting them from a further outbound client, it
   will generate its own 407 response, which might have the appearance
   of forwarding the Proxy-Authenticate header field if both proxies use
   the same challenge set.

   Note that the parsing considerations for WWW-Authenticate apply to
   this header field as well; see Section 4.4 for details.

4.3.  Proxy-Authorization

   The "Proxy-Authorization" header field allows the client to identify
   itself (or its user) to a proxy that requires authentication.  Its
   value consists of credentials containing the authentication
   information of the client for the proxy and/or realm of the resource
   being requested.

     Proxy-Authorization = credentials



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   Unlike Authorization, the Proxy-Authorization header field applies
   only to the next inbound proxy that demanded authentication using the
   Proxy-Authenticate field.  When multiple proxies are used in a chain,
   the Proxy-Authorization header field is consumed by the first inbound
   proxy that was expecting to receive credentials.  A proxy MAY relay
   the credentials from the client request to the next proxy if that is
   the mechanism by which the proxies cooperatively authenticate a given
   request.

4.4.  WWW-Authenticate

   The "WWW-Authenticate" header field consists of at least one
   challenge that indicates the authentication scheme(s) and parameters
   applicable to the effective request URI (Section 5.5 of [Part1]).

   It MUST be included in 401 (Unauthorized) response messages and MAY
   be included in other response messages to indicate that supplying
   credentials (or different credentials) might affect the response.

     WWW-Authenticate = 1#challenge

   User agents are advised to take special care in parsing the field
   value, as it might contain more than one challenge, and each
   challenge can contain a comma-separated list of authentication
   parameters.  Furthermore, the header field itself can occur multiple
   times.

   For instance:

     WWW-Authenticate: Newauth realm="apps", type=1,
                       title="Login to \"apps\"", Basic realm="simple"

   This header field contains two challenges; one for the "Newauth"
   scheme with a realm value of "apps", and two additional parameters
   "type" and "title", and another one for the "Basic" scheme with a
   realm value of "simple".

      Note: The challenge grammar production uses the list syntax as
      well.  Therefore, a sequence of comma, whitespace, and comma can
      be considered either as applying to the preceding challenge, or to
      be an empty entry in the list of challenges.  In practice, this
      ambiguity does not affect the semantics of the header field value
      and thus is harmless.








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5.  IANA Considerations

5.1.  Authentication Scheme Registry

   The HTTP Authentication Scheme Registry defines the name space for
   the authentication schemes in challenges and credentials.  It will be
   created and maintained at (the suggested URI)
   <http://www.iana.org/assignments/http-authschemes>.

5.1.1.  Procedure

   Registrations MUST include the following fields:

   o  Authentication Scheme Name

   o  Pointer to specification text

   o  Notes (optional)

   Values to be added to this name space require IETF Review (see
   [RFC5226], Section 4.1).

5.1.2.  Considerations for New Authentication Schemes

   There are certain aspects of the HTTP Authentication Framework that
   put constraints on how new authentication schemes can work:

   o  HTTP authentication is presumed to be stateless: all of the
      information necessary to authenticate a request MUST be provided
      in the request, rather than be dependent on the server remembering
      prior requests.  Authentication based on, or bound to, the
      underlying connection is outside the scope of this specification
      and inherently flawed unless steps are taken to ensure that the
      connection cannot be used by any party other than the
      authenticated user (see Section 2.3 of [Part1]).

   o  The authentication parameter "realm" is reserved for defining
      Protection Spaces as defined in Section 2.2.  New schemes MUST NOT
      use it in a way incompatible with that definition.

   o  The "token68" notation was introduced for compatibility with
      existing authentication schemes and can only be used once per
      challenge or credential.  New schemes thus ought to use the "auth-
      param" syntax instead, because otherwise future extensions will be
      impossible.

   o  The parsing of challenges and credentials is defined by this
      specification, and cannot be modified by new authentication



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      schemes.  When the auth-param syntax is used, all parameters ought
      to support both token and quoted-string syntax, and syntactical
      constraints ought to be defined on the field value after parsing
      (i.e., quoted-string processing).  This is necessary so that
      recipients can use a generic parser that applies to all
      authentication schemes.

      Note: The fact that the value syntax for the "realm" parameter is
      restricted to quoted-string was a bad design choice not to be
      repeated for new parameters.

   o  Definitions of new schemes ought to define the treatment of
      unknown extension parameters.  In general, a "must-ignore" rule is
      preferable over "must-understand", because otherwise it will be
      hard to introduce new parameters in the presence of legacy
      recipients.  Furthermore, it's good to describe the policy for
      defining new parameters (such as "update the specification", or
      "use this registry").

   o  Authentication schemes need to document whether they are usable in
      origin-server authentication (i.e., using WWW-Authenticate),
      and/or proxy authentication (i.e., using Proxy-Authenticate).

   o  The credentials carried in an Authorization header field are
      specific to the User Agent, and therefore have the same effect on
      HTTP caches as the "private" Cache-Control response directive
      (Section 5.2.2.6 of [Part6]), within the scope of the request they
      appear in.

      Therefore, new authentication schemes that choose not to carry
      credentials in the Authorization header field (e.g., using a newly
      defined header field) will need to explicitly disallow caching, by
      mandating the use of either Cache-Control request directives
      (e.g., "no-store", Section 5.2.1.5 of [Part6]) or response
      directives (e.g., "private").

5.2.  Status Code Registration

   The HTTP Status Code Registry located at
   <http://www.iana.org/assignments/http-status-codes> shall be updated
   with the registrations below:










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   +-------+-------------------------------+-------------+
   | Value | Description                   | Reference   |
   +-------+-------------------------------+-------------+
   | 401   | Unauthorized                  | Section 3.1 |
   | 407   | Proxy Authentication Required | Section 3.2 |
   +-------+-------------------------------+-------------+

5.3.  Header Field Registration

   HTTP header fields are registered within the Message Header Field
   Registry maintained at <http://www.iana.org/assignments/
   message-headers/message-header-index.html>.

   This document defines the following HTTP header fields, so their
   associated registry entries shall be updated according to the
   permanent registrations below (see [BCP90]):

   +---------------------+----------+----------+-------------+
   | Header Field Name   | Protocol | Status   | Reference   |
   +---------------------+----------+----------+-------------+
   | Authorization       | http     | standard | Section 4.1 |
   | Proxy-Authenticate  | http     | standard | Section 4.2 |
   | Proxy-Authorization | http     | standard | Section 4.3 |
   | WWW-Authenticate    | http     | standard | Section 4.4 |
   +---------------------+----------+----------+-------------+

   The change controller is: "IETF (iesg@ietf.org) - Internet
   Engineering Task Force".

6.  Security Considerations

   This section is meant to inform developers, information providers,
   and users of known security concerns specific to HTTP/1.1
   authentication.  More general security considerations are addressed
   in HTTP messaging [Part1] and semantics [Part2].

6.1.  Authentication Credentials and Idle Clients

   Existing HTTP clients and user agents typically retain authentication
   information indefinitely.  HTTP does not provide a mechanism for the
   origin server to direct clients to discard these cached credentials,
   since the protocol has no awareness of how credentials are obtained
   or managed by the user agent.  The mechanisms for expiring or
   revoking credentials can be specified as part of an authentication
   scheme definition.

   Circumstances under which credential caching can interfere with the
   application's security model include but are not limited to:



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   o  Clients that have been idle for an extended period, following
      which the server might wish to cause the client to re-prompt the
      user for credentials.

   o  Applications that include a session termination indication (such
      as a "logout" or "commit" button on a page) after which the server
      side of the application "knows" that there is no further reason
      for the client to retain the credentials.

   User agents that cache credentials are encouraged to provide a
   readily accessible mechanism for discarding cached credentials under
   user control.

6.2.  Protection Spaces

   Authentication schemes that solely rely on the "realm" mechanism for
   establishing a protection space will expose credentials to all
   resources on an origin server.  Clients that have successfully made
   authenticated requests with a resource can use the same
   authentication credentials for other resources on the same origin
   server.  This makes it possible for a different resource to harvest
   authentication credentials for other resources.

   This is of particular concern when an origin server hosts resources
   for multiple parties under the same canonical root URI (Section 2.2).
   Possible mitigation strategies include restricting direct access to
   authentication credentials (i.e., not making the content of the
   Authorization request header field available), and separating
   protection spaces by using a different host name (or port number) for
   each party.

7.  Acknowledgments

   This specification takes over the definition of the HTTP
   Authentication Framework, previously defined in RFC 2617.  We thank
   John Franks, Phillip M. Hallam-Baker, Jeffery L. Hostetler, Scott D.
   Lawrence, Paul J. Leach, Ari Luotonen, and Lawrence C. Stewart for
   their work on that specification.  See Section 6 of [RFC2617] for
   further acknowledgements.

   See Section 10 of [Part1] for the Acknowledgments related to this
   document revision.

8.  References







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8.1.  Normative References

   [Part1]    Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              draft-ietf-httpbis-p1-messaging-25 (work in progress),
              November 2013.

   [Part2]    Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content",
              draft-ietf-httpbis-p2-semantics-25 (work in progress),
              November 2013.

   [Part6]    Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
              draft-ietf-httpbis-p6-cache-25 (work in progress),
              November 2013.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

8.2.  Informative References

   [BCP90]    Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              September 2004.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [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, June 1999.

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

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.



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Appendix A.  Changes from RFCs 2616 and 2617

   The framework for HTTP Authentication is now defined by this
   document, rather than RFC 2617.

   The "realm" parameter is no longer always required on challenges;
   consequently, the ABNF allows challenges without any auth parameters.
   (Section 2)

   The "token68" alternative to auth-param lists has been added for
   consistency with legacy authentication schemes such as "Basic".
   (Section 2)

   This specification introduces the Authentication Scheme Registry,
   along with considerations for new authentication schemes.
   (Section 5.1)

Appendix B.  Imported ABNF

   The following core rules are included by reference, as defined in
   Appendix B.1 of [RFC5234]: ALPHA (letters), CR (carriage return),
   CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double
   quote), HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any
   8-bit sequence of data), SP (space), and VCHAR (any visible US-ASCII
   character).

   The rules below are defined in [Part1]:

     BWS           = <BWS, defined in [Part1], Section 3.2.3>
     OWS           = <OWS, defined in [Part1], Section 3.2.3>
     quoted-string = <quoted-string, defined in [Part1], Section 3.2.6>
     token         = <token, defined in [Part1], Section 3.2.6>

Appendix C.  Collected ABNF

   In the collected ABNF below, list rules are expanded as per Section
   1.2 of [Part1].














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   Authorization = credentials

   BWS = <BWS, defined in [Part1], Section 3.2.3>

   OWS = <OWS, defined in [Part1], Section 3.2.3>

   Proxy-Authenticate = *( "," OWS ) challenge *( OWS "," [ OWS
    challenge ] )
   Proxy-Authorization = credentials

   WWW-Authenticate = *( "," OWS ) challenge *( OWS "," [ OWS challenge
    ] )

   auth-param = token BWS "=" BWS ( token / quoted-string )
   auth-scheme = token

   challenge = auth-scheme [ 1*SP ( token68 / [ ( "," / auth-param ) *(
    OWS "," [ OWS auth-param ] ) ] ) ]
   credentials = auth-scheme [ 1*SP ( token68 / [ ( "," / auth-param )
    *( OWS "," [ OWS auth-param ] ) ] ) ]

   quoted-string = <quoted-string, defined in [Part1], Section 3.2.6>

   token = <token, defined in [Part1], Section 3.2.6>
   token68 = 1*( ALPHA / DIGIT / "-" / "." / "_" / "~" / "+" / "/" )
    *"="

Appendix D.  Change Log (to be removed by RFC Editor before publication)

   Changes up to the IETF Last Call draft are summarized in <http://
   trac.tools.ietf.org/html/draft-ietf-httpbis-p7-auth-24#appendix-D>.

D.1.  Since draft-ietf-httpbis-p7-auth-24

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/510>: "SECDIR review
      of draft-ietf-httpbis-p7-auth-24"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/513>: "APPSDIR
      review of draft-ietf-httpbis-p7-auth-24"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/516>: "note about
      WWW-A parsing potentially misleading"







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Index

   4
      401 Unauthorized (status code)  7
      407 Proxy Authentication Required (status code)  7

   A
      Authorization header field  7

   C
      Canonical Root URI  6

   G
      Grammar
         auth-param  5
         auth-scheme  5
         Authorization  8
         challenge  5
         credentials  5
         Proxy-Authenticate  8
         Proxy-Authorization  8
         token68  5
         WWW-Authenticate  9

   P
      Protection Space  6
      Proxy-Authenticate header field  8
      Proxy-Authorization header field  8

   R
      Realm  6

   W
      WWW-Authenticate header field  9

Authors' Addresses

   Roy T. Fielding (editor)
   Adobe Systems Incorporated
   345 Park Ave
   San Jose, CA  95110
   USA

   EMail: fielding@gbiv.com
   URI:   http://roy.gbiv.com/






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   Julian F. Reschke (editor)
   greenbytes GmbH
   Hafenweg 16
   Muenster, NW  48155
   Germany

   EMail: julian.reschke@greenbytes.de
   URI:   http://greenbytes.de/tech/webdav/











































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