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Versions: 00 01 02

Internet Engineering Task Force                                  Y. Oiwa
Internet-Draft                                               H. Watanabe
Intended status: Standards Track                               H. Takagi
Expires: April 27, 2012                                       RCIS, AIST
                                                               B. Kihara
                                                              T. Hayashi
                                                                 Lepidum
                                                                 Y. Ioku
                                                            Yahoo! Japan
                                                        October 25, 2011


         HTTP Authentication Extensions for Interactive Clients
                   draft-oiwa-http-auth-extension-00

Abstract

   This document specifies an extension of HTTP authentication framework
   for use with interactive clients.  Recently, the fundamental features
   of HTTP-level authentication is not enough for complex requirements
   of various Web-based applications.  This makes these applications to
   implement their own authentication frameworks using HTML Forms and
   other means, which becomes one of the hurdles against introducing
   secure authentication mechanisms handled jointly by servers and user-
   agent clients.  The extended framework fills gaps between Web
   application requirements and HTTP authentication provisions to solve
   the above problems, while maintaining some upper-compatibility
   against existing Web and non-Web uses of HTTP authentications.

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 April 27, 2012.

Copyright Notice




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   Copyright (c) 2011 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Terms for describing authentication protocol flow  . . . .  4
     2.2.  Syntax Notation  . . . . . . . . . . . . . . . . . . . . .  6
   3.  Optional Authentication  . . . . . . . . . . . . . . . . . . .  7
   4.  Authentication-Control header  . . . . . . . . . . . . . . . .  9
     4.1.  Auth-style parameter . . . . . . . . . . . . . . . . . . .  9
     4.2.  Location-when-unauthenticated parameter  . . . . . . . . . 10
     4.3.  No-auth parameter  . . . . . . . . . . . . . . . . . . . . 11
     4.4.  Location-when-logout parameter . . . . . . . . . . . . . . 12
     4.5.  Logout-timeout . . . . . . . . . . . . . . . . . . . . . . 12
   5.  Usage examples [TBD] . . . . . . . . . . . . . . . . . . . . . 13
   6.  Methods to extend this protocol  . . . . . . . . . . . . . . . 13
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Appendix A.  (Informative) Applicability of features for each
                messages  . . . . . . . . . . . . . . . . . . . . . . 15
   Appendix B.  (Informative) Draft Notes . . . . . . . . . . . . . . 15
   Appendix C.  (Informative) Draft Change Log  . . . . . . . . . . . 16
     C.1.  Changes in revision 00 . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16










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1.  Introduction

   The document proposes several extensions to the current HTTP
   authentication framework, to provide enough functionality comparable
   with current widely-used form-based Web authentication.  A majority
   of the recent Web-sites on the Internet use custom application-layer
   authentication implementations using Web forms.  The reasons for
   these may vary, but many people believe that the current HTTP Basic
   (and Digest, too) authentication method does not have enough
   functionality (including a good-feeling user interfaces) to support
   most of realistic Web-based applications.  However, the method is
   very weak against phishing attacks, because the whole behavior of the
   authentication is controlled from the server side.  To overcome this
   problem, we need to "modernize" the HTTP authentication framework so
   that better client-controlled secure methods can be used with Web
   applications.  The extensions proposed in this document include:

   o  non-mandatory, optional authentication on HTTP (Section 3),

   o  log out from both server and client side (Section 4), and

   o  finer control for redirection depending on authentication status
      (Section 4).

   [I-D note: These extensions are initially proposed as a part of
   [I-D.oiwa-http-mutualauth].  However, since these might possibly be
   useful in combination with other authentication schemes, the
   extensions were separated as an independent draft.]

1.1.  Terminology

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

   The terms "encouraged" and "advised" are used for suggestions that do
   not constitute "SHOULD"-level requirements.  People MAY freely choose
   not to include the suggested items regarding [RFC2119], but complying
   with those suggestions would be a best practice; it will improve the
   security, interoperability, and/or operational performance.

   This document distinguishes the terms "client" and "user" in the
   following way: A "client" is an entity understanding and talking HTTP
   and the specified authentication protocol, usually computer software;
   a "user" is a (usually natural) person who wants to access data
   resources using "a client".




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2.  Definitions

2.1.  Terms for describing authentication protocol flow

   HTTP Authentication defined in [I-D.ietf-httpbis-p7-auth] may involve
   with several pairs of HTTP requests/responses.  Throughout this
   document, the following terms are used to categorize those messages:
   for requests,

   o  A non-authenticating request is a request not attempting any
      authentication: a request without any Authorization header.

   o  An authenticating request is the opposite: a request with an
      Authorization header.

   For responses,

   1) A non-authenticated response:  is a response which does not
      involve with any HTTP authentication.  It may not contain any
      WWW-Authenticate or Authentication-Info header.

      Servers send this response when the requested resource is not
      protected by HTTP authentication mechanisms.  In context of this
      specification, not-authentication-related negative responses (e.g.
      403 and 404) are also considered as non-authenticated responses.

      (See note on successfully-authenticated responses below for some
      ambiguous cases.)

   2) An authentication-initializing response:  is a response which
      requires or allows clients to start authentication attempts.
      Servers send this response when the requested resource is
      protected by HTTP authentication mechanism, and the request meets
      one of the following cases:

      *  The request is non-authenticating request, or

      *  The request contained an authentication trial directed to the
         protection space (realm) other than the server's expected one.

      The server will specify the protection space for authentication in
      this response.

      Upon reception, the client's behavior is further divided to two
      possible cases.

      *  If the client may have no prior knowledge on authentication
         credentials (e.g. a user-name and a password) related to the



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         requested protection space, the protocol flow terminates and
         the client will ask the user to provide authentication
         credentials,

      *  On the other hand, if client already have an enough credentials
         for authentication to the requested protection space, the
         client will automatically send an authenticating request.  Such
         cases often occur when the client did not know beforehand that
         the current request-URL requires an authentication.

   3) A successfully-authenticated response:  is a response for an
      authenticating request meaning that the authentication attempt was
      granted.  (Note: if the authentication scheme used does not use an
      Authentication-Info header, it may be indistinguishable from a
      non-authenticated response.)

   4) An intermediate authenticating response:  is a response for an
      authenticating request which requires some more reaction by the
      client software without involving users.  Such a response is
      required when an authentication scheme requires two or more round-
      trip messages to perform authentication, or when an authentication
      scheme uses some speculative short-cut method (such as uses of
      cached shared secrets) and it failed.

   5) A negatively-authenticated response:  is a response for an
      authenticating request which means that the authentication attempt
      was declined and can not continue without another authentication
      credential.  Clients typically erase memory of the currently-using
      credentials and ask the user for other ones.

      Usually the format of these responses are as same as the one for
      authentication-initializing responses.  Client can distinguish it
      by comparing the protection spaces contained in the request and in
      the response.

   Figure 1 shows a state diagram of generic HTTP authentication with
   the above message categorization.  Note that many authentication
   schemes uses only a subset of the transitions described on the
   diagram.  Labels in the figure show the abbreviated names of response
   types.











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         ===========                                -----------------
         NEW REQUEST                               ( UNAUTHENTICATED )
         ===========                                -----------------
              |                                            ^ non-auth.
              v                                            | response
   +----------------------+ NO                         +-------------+
   | The requested URI    |--------------------------->| send normal |
   | known to be auth'ed? |           ---------------->|   request   |
   +----------------------+          /                 +-------------+
          YES |                     /             initializing|
              v                    /                          |
     +------------------+ NO      /                           |
     | Can auth-req (*1)|---------                            |
     | be constructed?  |                                     |
     +------------------+                                     |
          YES |            initializing                       |
              |      ---------------------------------------. |
              |     /                                       v v
              |    |            ----------------    NO  +-----------+
              |    |           ( AUTH-REQUESTED )<------|credentials|
              |    |            ----------------        |   known?  |
              v    |                                    +-----------+
        +-----------+ negative   -------------   negative     |YES
        |   send    |---------->( AUTH-FAILED )<---------,    |
       /| auth-req  |            -------------           |    |
      / +-----------+\                                   |    v
     |             \  \  intermediate                   +-----------+
     |              \  -------------------------------->|   send    |
     |               \                                  | auth-req  |
     | non-auth.      \successful            successful +-----------+
     | response (*2)   \                               /     |    ^
     v                  \                             /      |    |
    -----------------    \       --------------      /       `----'
   ( UNAUTHENTICATED )    ----->( AUTH-SUCCEED )<----    intermediate
    -----------------            --------------


          Figure 1: Generic state diagram for HTTP authentication

   Note: (*1) For example, "Digest" scheme requires server-provided
   nonces to construct client-side challenges.
   (*2) In "Basic" and some others, this cannot be distinguished from a
   successfully-authenticated response.

2.2.  Syntax Notation

   This specification uses an extended BNF syntax defined in
   [I-D.ietf-httpbis-p1-messaging].  The following syntax definitions



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   are quoted from [I-D.ietf-httpbis-p1-messaging] and
   [I-D.ietf-httpbis-p7-auth]: auth-scheme, quoted-string, auth-param,
   SP, header-field, and challenge.  It also uses the convention of
   using header names for specifying syntax of header values.

   Additionally, this specification uses the following syntax elements
   following syntax definitions as a refinement for token and the
   righthand-side of auth-param in [I-D.ietf-httpbis-p7-auth].  Note
   that bare-token, extension-token and integer are subset of the
   token's syntax, and the extension-param is a subset of auth-param.
   (Note: these definitions are consistent with those in
   [I-D.oiwa-http-mutualauth].)

    bare-token        = 1*(%x30-39 / %x41-5A / %x61-7A / "-" / "_")
    extension-token   = "-" bare-token 1*("." bare-token)
    extension-param   = (bare-token / extension-token) "=" value
    value             = bare-token / extension-token / quoted-string
    integer           = "0" / (%x31-39 *%x30-39)      ; no leading zeros

               Figure 2: the BNF syntax for common notations

   Extensive-tokens are used in this protocol where the set of
   acceptable tokens may include private extensions.  Any private
   extensions of this protocol MUST use the extension-tokens with format
   "-<token>.<domain-name>", where <domain-name> is a validly registered
   (sub-)domain name on the Internet owned by the party who defines the
   extensions.


3.  Optional Authentication

   The Optional-WWW-Authenticate header enables a non-mandatory
   authentication, which is not possible under the current HTTP
   authentication mechanism.  In several Web applications, users can
   access the same contents as both a guest user and an authenticated
   user.  In most Web applications, it is implemented using HTTP cookies
   [RFC6265] and custom form-based authentications.  The new
   authentication method using this message will provide a replacement
   for these authentication systems.

   Servers MAY send HTTP successful responses (response code 200, 206
   and others) containing the Optional-WWW-Authenticate header as a
   replacement of a 401 response when it is an authentication-
   initializing response.  The Optional-WWW-Authenticate header MUST NOT
   be contained in 401 responses.






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      HTTP/1.1 200 OK
      Optional-WWW-Authenticate: Basic realm="xxxx"


    Optional-WWW-Authenticate = challenge

         Figure 3: BNF syntax for Optional-WWW-Authenticate header

   The challenge contained in the Optional-WWW-Authenticate header are
   the same as those for a 401 responses corresponding for a same
   request.  For authentication-related matters, an optional
   authentication request will have the same meaning as a 401 message
   with a corresponding WWW-Authenticate header (as an authentication-
   initializing response).  (The behavior for other matters, such as
   caching, MAY be different between the optional authentication and 401
   messages.)

   A response with an Optional-WWW-Authenticate header SHOULD be
   returned from the server only when the request is either non-
   authenticated or authenticating to a wrong (not the server's
   expected) protection space.  If a response is either an intermediate
   or a negative response to a client's authentication attempt, the
   server MUST respond with a 401 status response with a
   WWW-Authenticate header instead.  Failure to comply this rule will
   make client not able to distinguish authentication successes and
   failures.

   The server is NOT RECOMMENDED to include an Optional-WWW-Authenticate
   header in a positive response when a client's authentication attempt
   succeeds.

   Whenever an authentication scheme support for servers to send some
   parameter which gives a hint of URL space for the corresponding
   protection space for the same realm (e.g. "path" or "domain"),
   servers requesting non-mandatory authentication SHOULD send such
   parameter with the response.  Clients supporting non-mandatory
   authentication MUST recognize the parameter, and MUST send a request
   with an appropriate authentication credential in an Authorization
   header for any URI inside the specified paths.

   Support of this header is OPTIONAL; Clients MAY also choose any set
   of authentication schemes for which optional authentication is
   supported (in other words, its support MAY be scheme-dependent).
   However, some authentication schemes MAY require mandatory/
   recommended support for this header, so that server-side applications
   MAY assume that clients supporting such schemes are likely to support
   the extension as well.




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4.  Authentication-Control header

   Authentication-Control = auth-scheme 1*SP 1#Auth-Ctrl-params
   Auth-Ctrl-params  = auth-style / no-auth / loc-when-unauthed
                     / loc-when-logout / logout-timeout
                     / extension-param
   auth-style        = "auth-style" "=" ( "modal" / "non-modal" )
   no-auth           = "no-auth" "=" "true"
   loc-when-unauthed = "location-when-unauthenticated" "=" quoted-string
   loc-when-logout   = "location-when-logout" "=" quoted-string
   logout-timeout    = "logout-timeout" "=" integer

      Figure 4: the BNF syntax for the Authentication-Control header

   The Authentication-Control header provides a more precise control of
   the client behavior for Web applications using an HTTP authentication
   protocol.  This header is supposed to be generated in the application
   layer, as opposed to WWW-Authenticate headers which will be generated
   by the Web servers.

   Support of this header is OPTIONAL, and clients MAY choose any subset
   of these parameters to be supported.  The set of supported parameters
   MAY also be authentication scheme-dependent.  However, some
   authentication schemes MAY require mandatory/recommended support for
   some or all of the features provided in this header.

   The "auth-scheme" specified in this header and other authentication-
   related headers within the same message MUST be the same.  Clients
   MUST ignore any unknown parameters contained in this header.

   Server-side application SHOULD always be reminded that any parameters
   contained in this header MAY be ignored by clients.  Also, even when
   a client accepts this header, users may always be able to circumvent
   semantics of this header.  Therefore, if this header is used for
   security purposes, its use MUST be limited for providing some non-
   fundamental additional security measures valuable for end-users (such
   as client-side log-out for protecting against console takeover).
   Server-side application MUST NOT rely on the use of this header for
   protecting server-side resources.

4.1.  Auth-style parameter

   Authentication-Control: Digest auth-style=modal

   The parameter "auth-style" specifies the server's preferences over
   user interface behavior for user authentication.  This parameter can
   be included in any kind of responses, however, it is only meaningful
   for either authentication-initializing or negatively-authenticated



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   responses.  The value of this parameter MUST be one of the tokens
   "modal" or "non-modal".  When the Optional-WWW-Authenticate header is
   used, the value of this parameter MUST be disregarded and the value
   "non-modal" is implied.

   The value of "modal" means that the server thinks the content of the
   response (body and other content-related headers) is valuable only
   for users refusing authentication request.  The clients are expected
   to ask the user a password before processing the content.  This
   behavior is common for most of the current implementations of Basic
   and Digest authentication schemes.

   The value of "non-modal" means that the server thinks the content of
   the response (body and other content-related headers) is valuable for
   users before processing an authentication request.  The clients are
   expected to first process the content and then provide users
   opportunities to perform authentication.

   The default behavior for the clients is implementation-dependent, and
   clients MAY choose different defaults for different authentication
   schemes.  The proposed default behavior is "modal" for all
   authentication schemes, but specifications for authentication schemes
   MAY propose a different default.

   The above two different methods of authentication may introduce a
   observable difference of semantics when the response contains state-
   changing side effects; for example, it may change whether Cookie
   headers [RFC6265] in 401 responses are processed or not.  However,
   the server applications SHOULD NOT depend on both existence and non-
   existence of such side effects.

4.2.  Location-when-unauthenticated parameter

   Authentication-Control: Mutual
   location-when-unauthenticated="http://www.example.com/login.html"

   The parameter "location-when-unauthenticated" specifies a location
   where any unauthenticated clients should be redirected to.  This
   header may be used, for example, when there is a central login page
   for the entire Web application.  The value of this parameter MUST be
   a string that contains an absolute URL location.  If a given URL is
   not absolute, the clients MAY consider it a relative URL from the
   current location.

   This parameter MAY be used with a 401 response for authentication-
   initializing response.  It can also be contained, although
   NOT RECOMMENDED, in a positive response with an
   Optional-WWW-Authenticate header.  The clients MUST ignore this



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   parameter, when a response is either successfully-authenticated or
   intermediately-authenticated.  The clients SHOULD ignore this
   parameter when a response is a negatively-authenticated one (the case
   is unlikely to happen, though).

   When a client receives an authentication-initiating response with
   this parameter, if the client has to ask users for authentication
   credentials, the client will treat the entire response as if it were
   a 303 "See Other" response with a Location header that contains the
   value of this parameter (i.e., client will be redirected to the
   specified location with a GET request).  Unlike a normal 303
   response, if the client can process authentication without the user's
   interaction, this parameter MUST be ignored.

4.3.  No-auth parameter

   Authentication-Control: Basic no-auth=true

   The parameter "no-auth" is a variant of the
   location-when-unauthenticated parameter; it specifies that new
   authentication attempt is not to be performed on this location for
   better user experience, without specifying the redirection on the
   HTTP level.  This header may be used, for example, when there is a
   central login page for the entire Web application, and when a (Web
   content's level) explicit interaction of users is desired before
   authentications.  The value of this parameter MUST be a token "true".
   If the value is incorrect, client MAY ignore this parameter.

   This parameter MAY be used with authentication-initiating responses.
   It can also be contained, although NOT RECOMMENDED, in a positive
   response with an Optional-WWW-Authenticate header.  The clients MUST
   ignore this parameter, when a response is either successfully-
   authenticated or intermediately-authenticated.  The clients SHOULD
   ignore this parameter when a response is a negatively-authenticated
   one (the case is unlikely to happen, though).

   When a client receives an authentication-initiating response with
   this parameter, if the client has to ask users for authentication
   credentials, the client will ignore the WWW-Authenticate header
   contained in the response and treat the whole response as a normal
   negative 4xx-class response instead of giving user an opportunity to
   start authentication.  If the client can process authentication
   without the user's interaction, this parameter MUST ignored.

   This parameter SHOULD NOT be used along with the
   location-when-unauthenticated parameter.  If both were supplied,
   clients MAY choose which one is to be honored.




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   This parameter SHOULD NOT be used as any security measures to prevent
   authentication attempts, as it is easily circumvented by users.  This
   parameter SHOULD be used solely for improving user experience of web
   applications.

4.4.  Location-when-logout parameter

   Authentication-Control: Digest
   location-when-logout="http://www.example.com/byebye.html"

   The parameter "location-when-logout" specifies a location where the
   client is to be redirected when the user explicitly request a logout.
   The value of this parameter MUST be a string that contains an
   absolute URL location.  If a given URL is not absolute, the clients
   MAY consider it a relative URL from the current location.

   This parameter MAY be used with successfully-authenticated responses.
   If this parameter is contained in other kinds of responses, the
   clients MUST ignore this parameter.

   When the user requests to terminate an authentication period, and if
   the client currently displays a page supplied by a response with this
   parameter, the client will be redirected to the specified location by
   a new GET request (as if it received a 303 response).  The log-out
   operation (e.g. erasing memories of user name, authentication
   credential and all related one-time credentials such as nonce or
   keys) SHOULD occur before processing a redirection.

   When the user requests to terminate an authentication period, if the
   client supports this parameter but the server response does not
   contain this parameter, the client's RECOMMENDED behavior is as
   follows: if the request corresponding to the current content was
   idempotent (e.g.  GET), reload the page without the authentication
   credential.  If the request was non-idempotent (e.g.  POST), keep the
   current content as-is and simply forget the authentication status.
   The client SHOULD NOT replay a non-idempotent request without the
   user's explicit approval.

   Web applications are encouraged to send this parameter with an
   appropriate value for any responses (except those with redirection
   (3XX) statuses) for non-GET requests.

4.5.  Logout-timeout

   Authentication-Control: Basic logout-timeout=300

   The parameter "logout-timeout", when contained in a successfully-
   authenticated response, means that any authentication credentials and



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   states related to the current protection space are to be discarded if
   a time specified in this header (in seconds) has been passed from the
   time received.  As a special case, the value of logout-timeout=0
   means that the client is requested to immediately log-out from the
   current authentication space and revert to an unauthenticated status.
   This does not, however, mean that the long-term memories for the
   passwords (such as the password reminders and auto fill-ins) should
   be removed.  If a new timeout value is received for the same
   authentication space, it cancels the previous timeout and sets a new
   timeout.


5.  Usage examples [TBD]

   [TBD]


6.  Methods to extend this protocol

   If a non-standard extension to this protocol is implemented, it MUST
   use the extension-param to avoid conflicts with this protocol and
   other future official extensions.

   Extension-tokens MAY be freely used for any non-standard, private,
   and/or experimental uses.  The extension-tokens MUST be with format
   "-<bare-token>.<domain-name>", where <domain-name> is a validly
   registered (sub-)domain name on the Internet owned by the party who
   defines the extensions.


7.  IANA Considerations

   Tokens used for the authentication control parameters may be either
   extension-tokens or bare-tokens as outlined in Section 2.2.  When
   bare-tokens are used in this protocol, these MUST be allocated by
   IANA.  Any tokens used for non-private, non-experimental parameters
   are RECOMMENDED to be registered to IANA, regardless of the kind of
   tokens used.

   To acquire registered tokens, a specification for the use of such
   tokens MUST be available as a publicly-accessible documents, as
   outlined as "Specification Required" level in [RFC5226].

   Note: More formal declarations will be added in the future drafts to
   meet the RFC 5226 requirements.






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8.  Security Considerations

   The purpose of the log-out timeout feature in the Authentication-
   control header is to protect users of clients from impersonation
   caused by an attacker having access to the same console.  Server
   application implementors SHOULD be aware that the directive may
   always be ignored by either malicious clients or clients not
   supporting this extension.  If the purpose of introducing a timeout
   for an authentication period is to protect server-side resources,
   such features MUST be implemented by other means such as HTTP Cookies
   [RFC6265].

   All parameters in Authentication-Control header SHOULD NOT be used
   for any security-enforcement purposes.  Server-side applications MUST
   be implemented always considering that the header may be either
   ignored by clients or even bypassed by users.


9.  References

9.1.  Normative References

   [I-D.ietf-httpbis-p1-messaging]
              Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
              Masinter, L., Leach, P., Berners-Lee, T., Reschke, J., and
              Y. Lafon, "HTTP/1.1, part 1: URIs, Connections, and
              Message Parsing", draft-ietf-httpbis-p1-messaging-16 (work
              in progress), August 2011.

   [I-D.ietf-httpbis-p7-auth]
              Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
              Masinter, L., Leach, P., Berners-Lee, T., Reschke, J., and
              Y. Lafon, "HTTP/1.1, part 7: Authentication",
              draft-ietf-httpbis-p7-auth-16 (work in progress),
              August 2011.

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

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

9.2.  Informative References

   [I-D.oiwa-http-mutualauth]
              Oiwa, Y., Watanabe, H., Ioku, Y., and T. Hayashi, "Mutual
              Authentication Protocol for HTTP",



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              draft-oiwa-http-mutualauth-09 (work in progress),
              July 2011.

   [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              April 2011.


Appendix A.  (Informative) Applicability of features for each messages

   This section provides cross-reference table about applicability of
   each features provided in this specification for each kinds of
   responses described in Section 2.1.  The table provided in this
   section is for informative purposes only.

        +-------------------+-------+----------+-----------+------+
        |                   | init. | success. | intermed. | neg. |
        +-------------------+-------+----------+-----------+------+
        | Optional auth.    | O     | n        | N         | N    |
        | auth-style        | O     | -        | -         | O    |
        | loc.-when-unauth. | O     | I        | I         | i    |
        | no-auth           | O     | I        | I         | i    |
        | loc.-when-logout  | -     | O        | -         | -    |
        | logout-timeout    | -     | O        | -         | -    |
        +-------------------+-------+----------+-----------+------+

   Legends:
   O = MAY contain; n = SHOULD NOT contain; N = MUST NOT contain
   i = SHOULD be ignored; I = MUST be ignored;
   - = meaningless (to be ignored)


Appendix B.  (Informative) Draft Notes

   Things which might be considered for future revisions:

   o  In [I-D.ietf-httpbis-p7-auth], meaning of WWW-Authenticate headers
      in non-401 responses are defined as "supplying credentials (or
      different credentials) might affect the response".  This
      clarification change leaves a way for using 200-status responses
      along with a WWW-Authenticate header for providing optional
      authentication.
      Incorporating this possibility, however, needs more detailed
      analysis on the behavior of existing clients and intermediate
      proxies for such possibly-confusing responses.  Optional-WWW-
      Authenticate is safer, at least for minimum backward
      compatibility, because clients not supporting this extension will
      consider this header as an unrecognized entity-header, possibly
      providing opportunity for silently falling-back to application-



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      level authentications.


Appendix C.  (Informative) Draft Change Log

C.1.  Changes in revision 00

   o  Separated from HTTP Mutual authentication proposal (-09).

   o  Adopting httpbis works as a referencing point to HTTP.

   o  Generalized, now applicable for all HTTP authentication schemes.

   o  Added "no-auth" and "auth-style" parameters.

   o  Loosened standardization requirements for parameter-name tokens
      registration.


Authors' Addresses

   Yutaka Oiwa
   National Institute of Advanced Industrial Science and Technology
   Research Center for Information Security
   Tsukuba Central 2
   1-1-1 Umezono
   Tsukuba-shi, Ibaraki
   JP

   Email: mutual-auth-contact@m.aist.go.jp


   Hajime Watanabe
   National Institute of Advanced Industrial Science and Technology


   Hiromitsu Takagi
   National Institute of Advanced Industrial Science and Technology


   Boku Kihara
   Lepidum Co. Ltd.
   #602, Village Sasazuka 3
   1-30-3 Sasazuka
   Shibuya-ku, Tokyo
   JP





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   Tatsuya Hayashi
   Lepidum Co. Ltd.


   Yuichi Ioku
   Yahoo! Japan, Inc.
   Midtown Tower
   9-7-1 Akasaka
   Minato-ku, Tokyo
   JP









































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