Hypertext Transfer Protocol (HTTP/1.1): Authentication

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](https://tools.ietf.org/html/rfc7230)], including the general    framework previously described in "HTTP Authentication: Basic and    Digest Access Authentication" [[RFC2617](https://tools.ietf.org/html/rfc2617)] and the related fields and    status codes previously defined in "Hypertext Transfer Protocol --    HTTP/1.1" [[RFC2616](https://tools.ietf.org/html/rfc2616)].     The IANA Authentication Scheme Registry ([Section 5.1](about:blank#section-5.1)) lists    registered authentication schemes and their corresponding    specifications, including the "basic" and "digest" authentication    schemes previously defined by [RFC 2617](https://tools.ietf.org/html/rfc2617).  

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](https://tools.ietf.org/html/rfc2119)].     Conformance criteria and considerations regarding error handling are    defined in [Section 2.5 of [RFC7230]](https://tools.ietf.org/html/rfc7230#section-2.5).  

This specification uses the Augmented Backus-Naur Form (ABNF)    notation of [[RFC5234](https://tools.ietf.org/html/rfc5234)] with a list extension, defined in [Section 7 of    [RFC7230]](https://tools.ietf.org/html/rfc7230#section-7), that allows for compact definition of comma-separated    lists using a '#' operator (similar to how the '\*' operator indicates    repetition).  [Appendix B](about:blank#appendix-B) describes rules imported from other    documents.  [Appendix C](about:blank#appendix-C) shows the collected grammar with all list    operators expanded to standard ABNF notation.  

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 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](https://tools.ietf.org/html/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](https://tools.ietf.org/html/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.      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](about:blank#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]](https://tools.ietf.org/html/rfc7231#section-6.5.3)).     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.  

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](https://tools.ietf.org/html/rfc7230#section-5.5) [5.5 of [RFC7230]](https://tools.ietf.org/html/rfc7230#section-5.5)) 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, 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.  

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](about:blank#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](about:blank#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.  

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](about:blank#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](about:blank#section-4.4)).   

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

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.   

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]](https://tools.ietf.org/html/rfc7234#section-3.2) for details of and    requirements pertaining to handling of the Authorization field by    HTTP caches.  

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]](https://tools.ietf.org/html/rfc7230#section-5.5)).  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](about:blank#section-4.1) for details.   

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.  

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](http://www.iana.org/assignments/http-authschemes)>.  

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](https://tools.ietf.org/html/rfc5226#section-4.1)).   

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]](https://tools.ietf.org/html/rfc7230#section-2.3)).     o  The authentication parameter "realm" is reserved for defining       protection spaces as described in [Section 2.2](about:blank#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).      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]](https://tools.ietf.org/html/rfc7234#section-5.2.2.6)), 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]](https://tools.ietf.org/html/rfc7234#section-5.2.1.5)) or response       directives (e.g., "private").  

The "Hypertext Transfer Protocol (HTTP) Status Code Registry" located    at <[http://www.iana.org/assignments/http-status-codes](http://www.iana.org/assignments/http-status-codes)> has been    updated with the registrations below:     +-------+-------------------------------+-------------+    | Value | Description                   | Reference   |    +-------+-------------------------------+-------------+    | 401   | Unauthorized                  | [Section 3.1](about:blank#section-3.1) |    | 407   | Proxy Authentication Required | [Section 3.2](about:blank#section-3.2) |    +-------+-------------------------------+-------------+  

HTTP header fields are registered within the "Message Headers"    registry maintained at    <[http://www.iana.org/assignments/message-headers/](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](about:blank#ref-BCP90)]).     +---------------------+----------+----------+-------------+    | Header Field Name   | Protocol | Status   | Reference   |    +---------------------+----------+----------+-------------+    | Authorization       | http     | standard | [Section 4.2](about:blank#section-4.2) |    | Proxy-Authenticate  | http     | standard | [Section 4.3](about:blank#section-4.3) |    | Proxy-Authorization | http     | standard | [Section 4.4](about:blank#section-4.4) |    | WWW-Authenticate    | http     | standard | [Section 4.1](about:blank#section-4.1) |    +---------------------+----------+----------+-------------+     The change controller is: "IETF (iesg@ietf.org) - Internet    Engineering Task Force".   

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](https://tools.ietf.org/html/rfc7230)] and semantics [[RFC7231](https://tools.ietf.org/html/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](about:blank#ref-OWASP)]), including common pitfalls for implementing and using the    authentication schemes found in practice.  

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](https://tools.ietf.org/html/rfc5246)]) prior to    exchanging any credentials.  

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:     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.  

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](about:blank#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.   

This specification takes over the definition of the HTTP    Authentication Framework, previously defined in [RFC 2617](https://tools.ietf.org/html/rfc2617).  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]](https://tools.ietf.org/html/rfc2617#section-6) for    further acknowledgements.     See [Section 10 of [RFC7230]](https://tools.ietf.org/html/rfc7230#section-10) for the Acknowledgments related to this    document revision.  

[[RFC2119]()]  Bradner, S., "Key words for use in RFCs to Indicate               Requirement Levels", [BCP 14](https://tools.ietf.org/html/bcp14), [RFC 2119](https://tools.ietf.org/html/rfc2119), March 1997.     [[RFC5234]()]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax               Specifications: ABNF", STD 68, [RFC 5234](https://tools.ietf.org/html/rfc5234), January 2008.     [[RFC7230]()]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer               Protocol (HTTP/1.1): Message Syntax and Routing",               [RFC 7230](https://tools.ietf.org/html/rfc7230), June 2014.     [[RFC7231]()]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer               Protocol (HTTP/1.1): Semantics and Content", [RFC 7231](https://tools.ietf.org/html/rfc7231),               June 2014.     [[RFC7234]()]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,               Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",               [RFC 7234](https://tools.ietf.org/html/rfc7234), June 2014.  

[[BCP90]()]    Klyne, G., Nottingham, M., and J. Mogul, "Registration               Procedures for Message Header Fields", [BCP 90](https://tools.ietf.org/html/bcp90), [RFC 3864](https://tools.ietf.org/html/rfc3864),               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/](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](https://tools.ietf.org/html/rfc2616), 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](https://tools.ietf.org/html/rfc2617), June 1999.     [[RFC3986]()]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform               Resource Identifier (URI): Generic Syntax", STD 66,               [RFC 3986](https://tools.ietf.org/html/rfc3986), January 2005.     [[RFC4648]()]  Josefsson, S., "The Base16, Base32, and Base64 Data               Encodings", [RFC 4648](https://tools.ietf.org/html/rfc4648), October 2006.     [[RFC5226]()]  Narten, T. and H. Alvestrand, "Guidelines for Writing an               IANA Considerations Section in RFCs", [BCP 26](https://tools.ietf.org/html/bcp26), [RFC 5226](https://tools.ietf.org/html/rfc5226),               May 2008.     [[RFC5246]()]  Dierks, T. and E. Rescorla, "The Transport Layer Security               (TLS) Protocol Version 1.2", [RFC 5246](https://tools.ietf.org/html/rfc5246), August 2008.   

The framework for HTTP Authentication is now defined by this    document, rather than [RFC 2617](https://tools.ietf.org/html/rfc2617).     The "realm" parameter is no longer always required on challenges;    consequently, the ABNF allows challenges without any auth parameters.    ([Section 2](about:blank#section-2))     The "token68" alternative to auth-param lists has been added for    consistency with legacy authentication schemes such as "Basic".    ([Section 2](about:blank#section-2))     This specification introduces the Authentication Scheme Registry,    along with considerations for new authentication schemes.    ([Section 5.1](about:blank#section-5.1))  

The following core rules are included by reference, as defined in    [Appendix B.1 of [RFC5234]](https://tools.ietf.org/html/rfc5234#appendix-B.1): 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](https://tools.ietf.org/html/rfc7230)]:       BWS           = <BWS, see [[RFC7230], Section 3.2.3](https://tools.ietf.org/html/rfc7230#section-3.2.3)>      OWS           = <OWS, see [[RFC7230], Section 3.2.3](https://tools.ietf.org/html/rfc7230#section-3.2.3)>      quoted-string = <quoted-string, see [[RFC7230], Section 3.2.6](https://tools.ietf.org/html/rfc7230#section-3.2.6)>      token         = <token, see [[RFC7230], Section 3.2.6](https://tools.ietf.org/html/rfc7230#section-3.2.6)>   

In the collected ABNF below, list rules are expanded as per [Section](https://tools.ietf.org/html/rfc7230#section-1.2) [1.2 of [RFC7230]](https://tools.ietf.org/html/rfc7230#section-1.2).     Authorization = credentials     BWS = <BWS, see [[RFC7230], Section 3.2.3](https://tools.ietf.org/html/rfc7230#section-3.2.3)>     OWS = <OWS, see [[RFC7230], Section 3.2.3](https://tools.ietf.org/html/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](https://tools.ietf.org/html/rfc7230#section-3.2.6)>     token = <token, see [[RFC7230], Section 3.2.6](https://tools.ietf.org/html/rfc7230#section-3.2.6)>    token68 = 1\*( ALPHA / DIGIT / "-" / "." / "\_" / "~" / "+" / "/" )     \*"="   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   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/](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/](http://greenbytes.de/tech/webdav/)   Fielding & Reschke           Standards Track                   [Page 19]