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rfc:rfc7235

Internet Engineering Task Force (IETF) R. Fielding, Ed. Request for Comments: 7235 Adobe Obsoletes: 2616 J. Reschke, Ed. Updates: 2617 greenbytes Category: Standards Track June 2014 ISSN: 2070-1721

       Hypertext Transfer Protocol (HTTP/1.1): Authentication

Abstract

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

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7235.

Copyright Notice

 Copyright (c) 2014 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.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this

Fielding & Reschke Standards Track [Page 1] RFC 7235 HTTP/1.1 Authentication June 2014

 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Table of Contents

 1. Introduction ....................................................3
    1.1. Conformance and Error Handling .............................3
    1.2. Syntax Notation ............................................3
 2. Access Authentication Framework .................................3
    2.1. Challenge and Response .....................................3
    2.2. Protection Space (Realm) ...................................5
 3. Status Code Definitions .........................................6
    3.1. 401 Unauthorized ...........................................6
    3.2. 407 Proxy Authentication Required ..........................6
 4. Header Field Definitions ........................................7
    4.1. WWW-Authenticate ...........................................7
    4.2. Authorization ..............................................8
    4.3. Proxy-Authenticate .........................................8
    4.4. Proxy-Authorization ........................................9
 5. IANA Considerations .............................................9
    5.1. Authentication Scheme Registry .............................9
         5.1.1. Procedure ...........................................9
         5.1.2. Considerations for New Authentication Schemes ......10
    5.2. Status Code Registration ..................................11
    5.3. Header Field Registration .................................11
 6. Security Considerations ........................................12
    6.1. Confidentiality of Credentials ............................12
    6.2. Authentication Credentials and Idle Clients ...............12
    6.3. Protection Spaces .........................................13
 7. Acknowledgments ................................................14
 8. References .....................................................14
    8.1. Normative References ......................................14
    8.2. Informative References ....................................14
 Appendix A. Changes from RFCs 2616 and 2617 .......................16
 Appendix B. Imported ABNF .........................................16
 Appendix C. Collected ABNF ........................................17
 Index .............................................................18

Fielding & Reschke Standards Track [Page 2] RFC 7235 HTTP/1.1 Authentication June 2014

1. Introduction

 HTTP provides a general framework for access control and
 authentication, via an extensible set of challenge-response
 authentication schemes, which can be used by a server to challenge a
 client request and by a client to provide authentication information.
 This document defines HTTP/1.1 authentication in terms of the
 architecture defined in "Hypertext Transfer Protocol (HTTP/1.1):
 Message Syntax and Routing" [RFC7230], including the general
 framework previously described in "HTTP Authentication: Basic and
 Digest Access Authentication" [RFC2617] and the related fields and
 status codes previously defined in "Hypertext Transfer Protocol --
 HTTP/1.1" [RFC2616].
 The IANA Authentication Scheme Registry (Section 5.1) lists
 registered authentication schemes and their corresponding
 specifications, including the "basic" and "digest" authentication
 schemes previously defined by 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 [RFC7230].

1.2. Syntax Notation

 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).  Appendix B describes rules imported from other
 documents.  Appendix C shows the collected grammar with all list
 operators expanded to standard ABNF notation.

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

Fielding & Reschke Standards Track [Page 3] RFC 7235 HTTP/1.1 Authentication June 2014

 authentication via that scheme.  The latter can be either a comma-
 separated list of parameters or a single sequence of characters
 capable of holding base64-encoded information.
 Authentication parameters are name=value pairs, where the name token
 is matched case-insensitively, and each parameter name MUST only
 occur once per challenge.
   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]).
 A 401 (Unauthorized) response message is used by an origin server to
 challenge the authorization of a user agent, including a
 WWW-Authenticate header field containing at least one challenge
 applicable to the requested resource.
 A 407 (Proxy Authentication Required) response message is used by a
 proxy to challenge the authorization of a client, including 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 a challenge that contains an
    unknown scheme.  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.

Fielding & Reschke Standards Track [Page 4] RFC 7235 HTTP/1.1 Authentication June 2014

 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.  Transmission of
 credentials within header field values implies significant security
 considerations regarding the confidentiality of the underlying
 connection, as described in Section 6.1.
   credentials = auth-scheme [ 1*SP ( token68 / #auth-param ) ]
 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 omits proxy credentials or
 contains invalid or partial proxy credentials, a proxy that requires
 authentication SHOULD generate a 407 (Proxy Authentication Required)
 response that contains a Proxy-Authenticate header field with at
 least one (possibly new) challenge applicable to the proxy.
 A server that receives valid credentials that are not adequate to
 gain access ought to respond with the 403 (Forbidden) status code
 (Section 6.5.3 of [RFC7231]).
 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.

2.2. Protection Space (Realm)

 The "realm" authentication parameter is reserved for use by
 authentication schemes that wish to indicate a 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 [RFC7230]) 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

Fielding & Reschke Standards Track [Page 5] RFC 7235 HTTP/1.1 Authentication June 2014

 spaces, each with its own authentication scheme and/or authorization
 database.  The realm value is a string, generally assigned by the
 origin server, that can have additional semantics specific to the
 authentication scheme.  Note that a response can have multiple
 challenges with the same auth-scheme but with 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
 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 server generating a 401 response MUST send
 a WWW-Authenticate header field (Section 4.1) 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 4.2).  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 it indicates that the client needs to
 authenticate itself in order to use a proxy.  The proxy MUST send a
 Proxy-Authenticate header field (Section 4.3) 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 4.4).

Fielding & Reschke Standards Track [Page 6] RFC 7235 HTTP/1.1 Authentication June 2014

4. Header Field Definitions

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

4.1. WWW-Authenticate

 The "WWW-Authenticate" header field indicates the authentication
 scheme(s) and parameters applicable to the target resource.
   WWW-Authenticate = 1#challenge
 A server generating a 401 (Unauthorized) response MUST send a
 WWW-Authenticate header field containing at least one challenge.  A
 server MAY generate a WWW-Authenticate header field in other response
 messages to indicate that supplying credentials (or different
 credentials) might affect the response.
 A proxy forwarding a response MUST NOT modify any WWW-Authenticate
 fields in that response.
 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.

Fielding & Reschke Standards Track [Page 7] RFC 7235 HTTP/1.1 Authentication June 2014

4.2. 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
 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).
 A proxy forwarding a request MUST NOT modify any Authorization fields
 in that request.  See Section 3.2 of [RFC7234] for details of and
 requirements pertaining to handling of the Authorization field by
 HTTP caches.

4.3. 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 [RFC7230]).  A proxy MUST send at least one Proxy-Authenticate
 header field in each 407 (Proxy Authentication Required) response
 that it generates.
   Proxy-Authenticate = 1#challenge
 Unlike WWW-Authenticate, the Proxy-Authenticate header field applies
 only to the next outbound client on the response chain.  This is
 because only the client that chose a given proxy is likely to have
 the credentials necessary for authentication.  However, when multiple
 proxies are used within the same administrative domain, such as
 office and regional caching proxies within a large corporate network,
 it is common for credentials to be generated by the user agent and
 passed through the hierarchy until consumed.  Hence, in such a
 configuration, it will appear as if Proxy-Authenticate is being
 forwarded because each proxy will send the same challenge set.
 Note that the parsing considerations for WWW-Authenticate apply to
 this header field as well; see Section 4.1 for details.

Fielding & Reschke Standards Track [Page 8] RFC 7235 HTTP/1.1 Authentication June 2014

4.4. 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
 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.

5. IANA Considerations

5.1. Authentication Scheme Registry

 The "Hypertext Transfer Protocol (HTTP) Authentication Scheme
 Registry" defines the namespace for the authentication schemes in
 challenges and credentials.  It has been created and is now
 maintained at <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 namespace require IETF Review (see
 [RFC5226], Section 4.1).

Fielding & Reschke Standards Track [Page 9] RFC 7235 HTTP/1.1 Authentication June 2014

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 [RFC7230]).
 o  The authentication parameter "realm" is reserved for defining
    protection spaces as described 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.  Thus, new schemes 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
    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 to a "must-understand" rule, 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).

Fielding & Reschke Standards Track [Page 10] RFC 7235 HTTP/1.1 Authentication June 2014

 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 [RFC7234]), within the scope of the request in
    which they appear.
    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 [RFC7234]) or response
    directives (e.g., "private").

5.2. Status Code Registration

 The "Hypertext Transfer Protocol (HTTP) Status Code Registry" located
 at <http://www.iana.org/assignments/http-status-codes> has been
 updated with the registrations below:
 +-------+-------------------------------+-------------+
 | 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 Headers"
 registry maintained at
 <http://www.iana.org/assignments/message-headers/>.
 This document defines the following HTTP header fields, so the
 "Permanent Message Header Field Names" registry has been updated
 accordingly (see [BCP90]).
 +---------------------+----------+----------+-------------+
 | Header Field Name   | Protocol | Status   | Reference   |
 +---------------------+----------+----------+-------------+
 | Authorization       | http     | standard | Section 4.2 |
 | Proxy-Authenticate  | http     | standard | Section 4.3 |
 | Proxy-Authorization | http     | standard | Section 4.4 |
 | WWW-Authenticate    | http     | standard | Section 4.1 |
 +---------------------+----------+----------+-------------+
 The change controller is: "IETF (iesg@ietf.org) - Internet
 Engineering Task Force".

Fielding & Reschke Standards Track [Page 11] RFC 7235 HTTP/1.1 Authentication June 2014

6. Security Considerations

 This section is meant to inform developers, information providers,
 and users of known security concerns specific to HTTP authentication.
 More general security considerations are addressed in HTTP messaging
 [RFC7230] and semantics [RFC7231].
 Everything about the topic of HTTP authentication is a security
 consideration, so the list of considerations below is not exhaustive.
 Furthermore, it is limited to security considerations regarding the
 authentication framework, in general, rather than discussing all of
 the potential considerations for specific authentication schemes
 (which ought to be documented in the specifications that define those
 schemes).  Various organizations maintain topical information and
 links to current research on Web application security (e.g.,
 [OWASP]), including common pitfalls for implementing and using the
 authentication schemes found in practice.

6.1. Confidentiality of Credentials

 The HTTP authentication framework does not define a single mechanism
 for maintaining the confidentiality of credentials; instead, each
 authentication scheme defines how the credentials are encoded prior
 to transmission.  While this provides flexibility for the development
 of future authentication schemes, it is inadequate for the protection
 of existing schemes that provide no confidentiality on their own, or
 that do not sufficiently protect against replay attacks.
 Furthermore, if the server expects credentials that are specific to
 each individual user, the exchange of those credentials will have the
 effect of identifying that user even if the content within
 credentials remains confidential.
 HTTP depends on the security properties of the underlying transport-
 or session-level connection to provide confidential transmission of
 header fields.  In other words, if a server limits access to
 authenticated users using this framework, the server needs to ensure
 that the connection is properly secured in accordance with the nature
 of the authentication scheme used.  For example, services that depend
 on individual user authentication often require a connection to be
 secured with TLS ("Transport Layer Security", [RFC5246]) prior to
 exchanging any credentials.

6.2. 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

Fielding & Reschke Standards Track [Page 12] RFC 7235 HTTP/1.1 Authentication June 2014

 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:
 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.

6.3. 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.

Fielding & Reschke Standards Track [Page 13] RFC 7235 HTTP/1.1 Authentication June 2014

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 [RFC7230] for the Acknowledgments related to this
 document revision.

8. References

8.1. Normative References

 [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.
 [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
            Protocol (HTTP/1.1): Message Syntax and Routing",
            RFC 7230, June 2014.
 [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
            Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
            June 2014.
 [RFC7234]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
            Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
            RFC 7234, June 2014.

8.2. Informative References

 [BCP90]    Klyne, G., Nottingham, M., and J. Mogul, "Registration
            Procedures for Message Header Fields", BCP 90, RFC 3864,
            September 2004.
 [OWASP]    van der Stock, A., Ed., "A Guide to Building Secure Web
            Applications and Web Services", The Open Web Application
            Security Project (OWASP) 2.0.1, July 2005,
            <https://www.owasp.org/>.
 [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.

Fielding & Reschke Standards Track [Page 14] RFC 7235 HTTP/1.1 Authentication June 2014

 [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.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246, August 2008.

Fielding & Reschke Standards Track [Page 15] RFC 7235 HTTP/1.1 Authentication June 2014

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 [RFC7230]:
   BWS           = <BWS, see [RFC7230], Section 3.2.3>
   OWS           = <OWS, see [RFC7230], Section 3.2.3>
   quoted-string = <quoted-string, see [RFC7230], Section 3.2.6>
   token         = <token, see [RFC7230], Section 3.2.6>

Fielding & Reschke Standards Track [Page 16] RFC 7235 HTTP/1.1 Authentication June 2014

Appendix C. Collected ABNF

 In the collected ABNF below, list rules are expanded as per Section
 1.2 of [RFC7230].
 Authorization = credentials
 BWS = <BWS, see [RFC7230], Section 3.2.3>
 OWS = <OWS, see [RFC7230], 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, see [RFC7230], Section 3.2.6>
 token = <token, see [RFC7230], Section 3.2.6>
 token68 = 1*( ALPHA / DIGIT / "-" / "." / "_" / "~" / "+" / "/" )
  *"="

Fielding & Reschke Standards Track [Page 17] RFC 7235 HTTP/1.1 Authentication June 2014

Index

 4
    401 Unauthorized (status code)  6
    407 Proxy Authentication Required (status code)  6
 A
    Authorization header field  8
 C
    Canonical Root URI  5
 G
    Grammar
       auth-param  4
       auth-scheme  4
       Authorization  8
       challenge  4
       credentials  5
       Proxy-Authenticate  8
       Proxy-Authorization  9
       token68  4
       WWW-Authenticate  7
 P
    Protection Space  5
    Proxy-Authenticate header field  8
    Proxy-Authorization header field  9
 R
    Realm  5
 W
    WWW-Authenticate header field  7

Fielding & Reschke Standards Track [Page 18] RFC 7235 HTTP/1.1 Authentication June 2014

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/
 Julian F. Reschke (editor)
 greenbytes GmbH
 Hafenweg 16
 Muenster, NW  48155
 Germany
 EMail: julian.reschke@greenbytes.de
 URI:   http://greenbytes.de/tech/webdav/

Fielding & Reschke Standards Track [Page 19]

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