Source: https://trac.ietf.org/trac/httpbis/browser/draft-ietf-httpbis/latest/p7-auth.html?rev=1530
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<title>HTTP/1.1, part 7: Authentication</title><script>
var docname = "draft-ietf-httpbis-p7-auth-latest";
content: "February 2012";
content: "Expires August 10, 2012";
<link rel="Chapter" title="2 Access Authentication Framework" href="#rfc.section.2">
<link rel="Appendix" title="A Changes from RFCs 2616 and 2617" href="#rfc.section.A">
<link href="p6-cache.html" rel="prev">
<meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.567, 2012-02-06 22:22:25, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/">
<meta name="dct.issued" scheme="ISO8601" content="2012-02-07">
<meta name="description" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 7 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 7 defines the HTTP Authentication framework.">
<td class="left">Updates: <a href="http://tools.ietf.org/html/rfc2617">2617</a> (if approved)
<td class="left">Expires: August 10, 2012</td>
<td class="right">February 7, 2012</td>
<p>Part 7 defines the HTTP Authentication framework.</p>
<p>The changes in this draft are summarized in <a href="#changes.since.18" title="Since draft-ietf-httpbis-p7-auth-18">Appendix&nbsp;C.20</a>.
<p>This Internet-Draft will expire on August 10, 2012.</p>
<li>2.&nbsp;&nbsp;&nbsp;<a href="#access.authentication.framework">Access Authentication Framework</a><ul>
<li>2.1&nbsp;&nbsp;&nbsp;<a href="#challenge.and.response">Challenge and Response</a></li>
<li>2.2&nbsp;&nbsp;&nbsp;<a href="#protection.space">Protection Space (Realm)</a></li>
<li>2.3&nbsp;&nbsp;&nbsp;<a href="#authentication.scheme.registry">Authentication Scheme Registry</a><ul>
<li>2.3.1&nbsp;&nbsp;&nbsp;<a href="#considerations.for.new.authentication.schemes">Considerations for New Authentication Schemes</a></li>
<li>3.1&nbsp;&nbsp;&nbsp;<a href="#status.401">401 Unauthorized</a></li>
<li>3.2&nbsp;&nbsp;&nbsp;<a href="#status.407">407 Proxy Authentication Required</a></li>
<li>4.&nbsp;&nbsp;&nbsp;<a href="#header.field.definitions">Header Field Definitions</a><ul>
<li>4.1&nbsp;&nbsp;&nbsp;<a href="#header.authorization">Authorization</a></li>
<li>4.2&nbsp;&nbsp;&nbsp;<a href="#header.proxy-authenticate">Proxy-Authenticate</a></li>
<li>4.3&nbsp;&nbsp;&nbsp;<a href="#header.proxy-authorization">Proxy-Authorization</a></li>
<li>4.4&nbsp;&nbsp;&nbsp;<a href="#header.www-authenticate">WWW-Authenticate</a></li>
<li>5.1&nbsp;&nbsp;&nbsp;<a href="#authentication.scheme.registration">Authenticaton Scheme Registry</a></li>
<li>5.2&nbsp;&nbsp;&nbsp;<a href="#status.code.registration">Status Code Registration</a></li>
<li>6.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul>
<li>6.1&nbsp;&nbsp;&nbsp;<a href="#auth.credentials.and.idle.clients">Authentication Credentials and Idle Clients</a></li>
<li>A.&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFCs 2616 and 2617</a></li>
<li>C.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.C.2">Since draft-ietf-httpbis-p7-auth-00</a></li>
<li>C.3&nbsp;&nbsp;&nbsp;<a href="#rfc.section.C.3">Since draft-ietf-httpbis-p7-auth-01</a></li>
<li>C.4&nbsp;&nbsp;&nbsp;<a href="#changes.since.02">Since draft-ietf-httpbis-p7-auth-02</a></li>
<li>C.5&nbsp;&nbsp;&nbsp;<a href="#changes.since.03">Since draft-ietf-httpbis-p7-auth-03</a></li>
<li>C.6&nbsp;&nbsp;&nbsp;<a href="#changes.since.04">Since draft-ietf-httpbis-p7-auth-04</a></li>
<li>C.7&nbsp;&nbsp;&nbsp;<a href="#changes.since.05">Since draft-ietf-httpbis-p7-auth-05</a></li>
<li>C.8&nbsp;&nbsp;&nbsp;<a href="#changes.since.06">Since draft-ietf-httpbis-p7-auth-06</a></li>
<li>C.9&nbsp;&nbsp;&nbsp;<a href="#changes.since.07">Since draft-ietf-httpbis-p7-auth-07</a></li>
<li>C.10&nbsp;&nbsp;&nbsp;<a href="#changes.since.08">Since draft-ietf-httpbis-p7-auth-08</a></li>
<li>C.11&nbsp;&nbsp;&nbsp;<a href="#changes.since.09">Since draft-ietf-httpbis-p7-auth-09</a></li>
<li>C.12&nbsp;&nbsp;&nbsp;<a href="#changes.since.10">Since draft-ietf-httpbis-p7-auth-10</a></li>
<li>C.13&nbsp;&nbsp;&nbsp;<a href="#changes.since.11">Since draft-ietf-httpbis-p7-auth-11</a></li>
<li>C.14&nbsp;&nbsp;&nbsp;<a href="#changes.since.12">Since draft-ietf-httpbis-p7-auth-12</a></li>
<li>C.15&nbsp;&nbsp;&nbsp;<a href="#changes.since.13">Since draft-ietf-httpbis-p7-auth-13</a></li>
<li>C.16&nbsp;&nbsp;&nbsp;<a href="#changes.since.14">Since draft-ietf-httpbis-p7-auth-14</a></li>
<li>C.17&nbsp;&nbsp;&nbsp;<a href="#changes.since.15">Since draft-ietf-httpbis-p7-auth-15</a></li>
<li>C.18&nbsp;&nbsp;&nbsp;<a href="#changes.since.16">Since draft-ietf-httpbis-p7-auth-16</a></li>
<li>C.19&nbsp;&nbsp;&nbsp;<a href="#changes.since.17">Since draft-ietf-httpbis-p7-auth-17</a></li>
<li>C.20&nbsp;&nbsp;&nbsp;<a href="#changes.since.18">Since draft-ietf-httpbis-p7-auth-18</a></li>
<p id="rfc.section.1.p.1">This document defines HTTP/1.1 access control and authentication. It includes the relevant parts of <cite title="Hypertext Transfer Protocol -- HTTP/1.1" id="rfc.xref.RFC2616.1">RFC 2616</cite> with only minor changes, plus the general framework for HTTP authentication, as previously defined in "HTTP Authentication:
Basic and Digest Access Authentication" (<a href="#RFC2617" id="rfc.xref.RFC2617.1"><cite title="HTTP Authentication: Basic and Digest Access Authentication">[RFC2617]</cite></a>).
provide authentication information. The "basic" and "digest" authentication schemes continue to be specified in <cite title="HTTP Authentication: Basic and Digest Access Authentication" id="rfc.xref.RFC2617.2">RFC 2617</cite>.
<p id="rfc.section.1.2.1.p.1">The core rules below are defined in <a href="#Part1" id="rfc.xref.Part1.3"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>:
<div id="rfc.figure.u.1"></div><pre class="inline"> <a href="#core.rules" class="smpl">BWS</a> = &lt;BWS, defined in <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#whitespace" title="Whitespace">Section 3.2.1</a>&gt;
<a href="#core.rules" class="smpl">OWS</a> = &lt;OWS, defined in <a href="#Part1" id="rfc.xref.Part1.5"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#whitespace" title="Whitespace">Section 3.2.1</a>&gt;
<a href="#core.rules" class="smpl">quoted-string</a> = &lt;quoted-string, defined in <a href="#Part1" id="rfc.xref.Part1.6"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#field.components" title="Field value components">Section 3.2.4</a>&gt;
<a href="#core.rules" class="smpl">token</a> = &lt;token, defined in <a href="#Part1" id="rfc.xref.Part1.7"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#field.components" title="Field value components">Section 3.2.4</a>&gt;
</pre><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="access.authentication.framework" href="#access.authentication.framework">Access Authentication Framework</a></h1>
<h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="challenge.and.response" href="#challenge.and.response">Challenge and Response</a></h2>
<p id="rfc.section.2.1.p.1">HTTP provides a simple challenge-response authentication mechanism that can be used by a server to challenge a client request
and by a client to provide authentication information. It uses an extensible, case-insensitive token to identify the authentication
scheme, followed by additional information necessary for achieving authentication via that scheme. The latter can either be
a comma-separated list of parameters or a single sequence of characters capable of holding base64-encoded information.
<p id="rfc.section.2.1.p.2">Parameters are name-value pairs where the name is matched case-insensitively, and each parameter name <em class="bcp14">MUST</em> only occur once per challenge.
<div id="rfc.figure.u.2"></div><pre class="inline"><span id="rfc.iref.a.1"></span><span id="rfc.iref.a.2"></span><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.b.1"></span><span id="rfc.iref.g.3"></span> auth-scheme = <a href="#core.rules" class="smpl">token</a>
auth-param = <a href="#core.rules" class="smpl">token</a> <a href="#core.rules" class="smpl">BWS</a> "=" <a href="#core.rules" class="smpl">BWS</a> ( <a href="#core.rules" class="smpl">token</a> / <a href="#core.rules" class="smpl">quoted-string</a> )
b64token = 1*( <a href="#notation" class="smpl">ALPHA</a> / <a href="#notation" class="smpl">DIGIT</a> /
</pre><p id="rfc.section.2.1.p.4">The "b64token" syntax allows the 66 unreserved URI characters (<a href="#RFC3986" id="rfc.xref.RFC3986.1"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>), 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 (<a href="#RFC4648" id="rfc.xref.RFC4648.1"><cite title="The Base16, Base32, and Base64 Data Encodings">[RFC4648]</cite></a>).
<p id="rfc.section.2.1.p.5">The 401 (Unauthorized) response message is used by an origin server to challenge the authorization of a user agent. This response <em class="bcp14">MUST</em> include a WWW-Authenticate header field containing at least one challenge applicable to the requested resource.
<p id="rfc.section.2.1.p.6">The 407 (Proxy Authentication Required) response message is used by a proxy to challenge the authorization of a client and <em class="bcp14">MUST</em> include a Proxy-Authenticate header field containing at least one challenge applicable to the proxy for the requested resource.
<div id="rfc.figure.u.3"></div><pre class="inline"><span id="rfc.iref.c.1"></span><span id="rfc.iref.g.4"></span> <a href="#challenge.and.response" class="smpl">challenge</a> = <a href="#challenge.and.response" class="smpl">auth-scheme</a> [ 1*<a href="#notation" class="smpl">SP</a> ( <a href="#challenge.and.response" class="smpl">b64token</a> / #<a href="#challenge.and.response" class="smpl">auth-param</a> ) ]
</pre><div class="note" id="rfc.section.2.1.p.8">
<p> <b>Note:</b> User agents will need to take special care in parsing the WWW-Authenticate and Proxy-Authenticate header field values because
they can contain more than one challenge, or if more than one of each is provided, since the contents of a challenge can itself
contain a comma-separated list of authentication parameters.
<div class="note" id="rfc.section.2.1.p.9">
<p> <b>Note:</b> Many browsers fail to parse challenges containing unknown schemes. A workaround for this problem is to list well-supported
schemes (such as "basic") first.
<p id="rfc.section.2.1.p.10">A user agent that wishes to authenticate itself with an origin server — usually, but not necessarily, after receiving a 401
(Unauthorized) — <em class="bcp14">MAY</em> do so by including an Authorization header field with the request.
<p id="rfc.section.2.1.p.11">A client that wishes to authenticate itself with a proxy — usually, but not necessarily, after receiving a 407 (Proxy Authentication
Required) — <em class="bcp14">MAY</em> do so by including a Proxy-Authorization header field with the request.
<p id="rfc.section.2.1.p.12">Both the Authorization field value and the Proxy-Authorization field value consist of credentials containing the authentication
information of the client for the realm of the resource being requested. The user agent <em class="bcp14">MUST</em> choose to use one of the challenges with the strongest auth-scheme it understands and request credentials from the user based
upon that challenge.
<div id="rfc.figure.u.4"></div><pre class="inline"><span id="rfc.iref.c.2"></span><span id="rfc.iref.g.5"></span> <a href="#challenge.and.response" class="smpl">credentials</a> = <a href="#challenge.and.response" class="smpl">auth-scheme</a> [ 1*<a href="#notation" class="smpl">SP</a> ( <a href="#challenge.and.response" class="smpl">b64token</a> / #<a href="#challenge.and.response" class="smpl">auth-param</a> ) ]
</pre><p id="rfc.section.2.1.p.14">If the origin server does not wish to accept the credentials sent with a request, it <em class="bcp14">SHOULD</em> return a 401 (Unauthorized) response. The response <em class="bcp14">MUST</em> include a WWW-Authenticate header field containing at least one (possibly new) challenge applicable to the requested resource.
<p id="rfc.section.2.1.p.15">If a proxy does not accept the credentials sent with a request, it <em class="bcp14">SHOULD</em> return a 407 (Proxy Authentication Required). The response <em class="bcp14">MUST</em> include a Proxy-Authenticate header field containing a (possibly new) challenge applicable to the proxy for the requested
<p id="rfc.section.2.1.p.16">The HTTP protocol does not restrict applications to this simple challenge-response mechanism for access authentication. Additional
mechanisms <em class="bcp14">MAY</em> be used, such as encryption 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.
<p id="rfc.section.2.1.p.17">Proxies <em class="bcp14">MUST</em> forward the WWW-Authenticate and Authorization headers unmodified and follow the rules found in <a href="#header.authorization" id="rfc.xref.header.authorization.1" title="Authorization">Section&nbsp;4.1</a>.
<h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a id="protection.space" href="#protection.space">Protection Space (Realm)</a></h2>
<p id="rfc.section.2.2.p.1">The authentication parameter realm is reserved for use by authentication schemes that wish to indicate the scope of protection.</p>
<p id="rfc.section.2.2.p.2">A <dfn>protection space</dfn> is defined by the canonical root URI (the scheme and authority components of the effective request URI; see <a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.8"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) of the server being accessed, in combination with the realm value if present. These realms allow the protected resources
on a server to be partitioned into a set of protection spaces, each with its own authentication scheme and/or authorization
database. The realm value is a string, generally assigned by the origin server, which can have additional semantics specific
to the authentication scheme. Note that there can be multiple challenges with the same auth-scheme but different realms.
<p id="rfc.section.2.2.p.3">The protection space determines the domain over which credentials can be automatically applied. If a prior request has been
authorized, the same credentials <em class="bcp14">MAY</em> be reused for all other requests within that protection space for a period of time determined by the authentication scheme,
parameters, and/or user preference. Unless otherwise defined by the authentication scheme, a single protection space cannot
extend outside the scope of its server.
<p id="rfc.section.2.2.p.4">For historical reasons, senders <em class="bcp14">MUST</em> only use 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.
<h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a>&nbsp;<a id="authentication.scheme.registry" href="#authentication.scheme.registry">Authentication Scheme Registry</a></h2>
<p id="rfc.section.2.3.p.1">The HTTP Authentication Scheme Registry defines the name space for the authentication schemes in challenges and credentials.</p>
<p id="rfc.section.2.3.p.2">Registrations <em class="bcp14">MUST</em> include the following fields:
<li>Authentication Scheme Name</li>
<li>Notes (optional)</li>
<p id="rfc.section.2.3.p.3">Values to be added to this name space are subject to IETF review (<a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).
<p id="rfc.section.2.3.p.4">The registry itself is maintained at &lt;<a href="http://www.iana.org/assignments/http-authschemes">http://www.iana.org/assignments/http-authschemes</a>&gt;.
<h3 id="rfc.section.2.3.1"><a href="#rfc.section.2.3.1">2.3.1</a>&nbsp;<a id="considerations.for.new.authentication.schemes" href="#considerations.for.new.authentication.schemes">Considerations for New Authentication Schemes</a></h3>
<p id="rfc.section.2.3.1.p.1">There are certain aspects of the HTTP Authentication Framework that put constraints on how new authentication schemes can
<p id="rfc.section.2.3.1.p.2"> </p>
<p>HTTP authentication is presumed to be stateless: all of the information necessary to authenticate a request <em class="bcp14">MUST</em> 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 <a href="p1-messaging.html#intermediaries" title="Intermediaries">Section 2.3</a> of <a href="#Part1" id="rfc.xref.Part1.9"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
<p>The authentication parameter "realm" is reserved for defining Protection Spaces as defined in <a href="#protection.space" title="Protection Space (Realm)">Section&nbsp;2.2</a>. New schemes <em class="bcp14">MUST NOT</em> use it in a way incompatible with that definition.
<p>The "b64token" notation was introduced for compatibility with existing authentication schemes and can only be used once per
challenge/credentials. New schemes thus ought to use the "auth-param" syntax instead, because otherwise future extensions
<p>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.
<p> <b>Note:</b> 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.
<p>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).
<p>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, within the scope of the request they appear in.
<p>Therefore, new authentication schemes which choose not to carry credentials in the Authorization header (e.g., using a newly
defined header) will need to explicitly disallow caching, by mandating the use of either Cache-Control request directives
(e.g., "no-store") or response directives (e.g., "private").
<div id="rfc.iref.12"></div>
<p id="rfc.section.3.1.p.1">The request requires user authentication. The response <em class="bcp14">MUST</em> include a WWW-Authenticate header field (<a href="#header.www-authenticate" id="rfc.xref.header.www-authenticate.1" title="WWW-Authenticate">Section&nbsp;4.4</a>) containing a challenge applicable to the target resource. The client <em class="bcp14">MAY</em> repeat the request with a suitable Authorization header field (<a href="#header.authorization" id="rfc.xref.header.authorization.2" title="Authorization">Section&nbsp;4.1</a>). If the request already included Authorization credentials, then the 401 response indicates that authorization has been
already attempted authentication at least once, then the user <em class="bcp14">SHOULD</em> be presented the representation that was given in the response, since that representation might include relevant diagnostic
<div id="rfc.iref.13"></div>
<p id="rfc.section.3.2.p.1">This code is similar to 401 (Unauthorized), but indicates that the client ought to first authenticate itself with the proxy.
The proxy <em class="bcp14">MUST</em> return a Proxy-Authenticate header field (<a href="#header.proxy-authenticate" id="rfc.xref.header.proxy-authenticate.1" title="Proxy-Authenticate">Section&nbsp;4.2</a>) containing a challenge applicable to the proxy for the target resource. The client <em class="bcp14">MAY</em> repeat the request with a suitable Proxy-Authorization header field (<a href="#header.proxy-authorization" id="rfc.xref.header.proxy-authorization.1" title="Proxy-Authorization">Section&nbsp;4.3</a>).
<h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="header.field.definitions" href="#header.field.definitions">Header Field Definitions</a></h1>
<p id="rfc.section.4.1.p.1">The "Authorization" header field allows a user agent to authenticate itself with a server — usually, but not necessarily,
after receiving a 401 (Unauthorized) response. Its value consists of credentials containing information of the user agent
for the realm of the resource being requested.
<div id="rfc.figure.u.5"></div><pre class="inline"><span id="rfc.iref.g.6"></span> <a href="#header.authorization" class="smpl">Authorization</a> = <a href="#challenge.and.response" class="smpl">credentials</a>
</pre><p id="rfc.section.4.1.p.3">If a request is authenticated and a realm specified, the same credentials <em class="bcp14">SHOULD</em> be valid for all other requests within this realm (assuming that the authentication scheme itself does not require otherwise,
<p id="rfc.section.4.1.p.4">When a shared cache (see <a href="p6-cache.html#shared.and.non-shared.caches">Section 1.2</a> of <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) receives a request containing an Authorization field, it <em class="bcp14">MUST NOT</em> return the corresponding response as a reply to any other request, unless one of the following specific exceptions holds:
<li>If the response includes the "s-maxage" cache-control directive, the cache <em class="bcp14">MAY</em> use that response in replying to a subsequent request. But (if the specified maximum age has passed) a proxy cache <em class="bcp14">MUST</em> first revalidate it with the origin server, using the header fields from the new request to allow the origin server to authenticate
<li>If the response includes the "must-revalidate" cache-control directive, the cache <em class="bcp14">MAY</em> use that response in replying to a subsequent request. But if the response is stale, all caches <em class="bcp14">MUST</em> first revalidate it with the origin server, using the header fields from the new request to allow the origin server to authenticate
<p id="rfc.section.4.2.p.1">The "Proxy-Authenticate" header field consists of a challenge that indicates the authentication scheme and parameters applicable
to the proxy for this effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.10"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>). It <em class="bcp14">MUST</em> be included as part of a 407 (Proxy Authentication Required) response.
<div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.7"></span> <a href="#header.proxy-authenticate" class="smpl">Proxy-Authenticate</a> = 1#<a href="#challenge.and.response" class="smpl">challenge</a>
</pre><p id="rfc.section.4.2.p.3">Unlike WWW-Authenticate, the Proxy-Authenticate header field applies only to the current connection and <em class="bcp14">SHOULD NOT</em> be passed on to downstream clients. However, an intermediate proxy might need to obtain its own credentials by requesting
<div id="rfc.iref.p.3"></div>
<p id="rfc.section.4.3.p.1">The "Proxy-Authorization" header field allows the client to identify itself (or its user) to a proxy which requires authentication.
Its value consists of credentials containing the authentication information of the user agent for the proxy and/or realm of
the resource being requested.
<div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.8"></span> <a href="#header.proxy-authorization" class="smpl">Proxy-Authorization</a> = <a href="#challenge.and.response" class="smpl">credentials</a>
</pre><p id="rfc.section.4.3.p.3">Unlike Authorization, the Proxy-Authorization header field applies only to the next outbound proxy that demanded authentication
<p id="rfc.section.4.4.p.1">The "WWW-Authenticate" header field consists of at least one challenge that indicates the authentication scheme(s) and parameters
applicable to the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.11"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
<p id="rfc.section.4.4.p.2">It <em class="bcp14">MUST</em> be included in 401 (Unauthorized) response messages and <em class="bcp14">MAY</em> be included in other response messages to indicate that supplying credentials (or different credentials) might affect the
<div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.9"></span> <a href="#header.www-authenticate" class="smpl">WWW-Authenticate</a> = 1#<a href="#challenge.and.response" class="smpl">challenge</a>
</pre><p id="rfc.section.4.4.p.4">User agents are advised to take special care in parsing the WWW-Authenticate field value as it might contain more than one
<div id="rfc.figure.u.9"></div>
<p>For instance:</p> <pre class="text"> WWW-Authenticate: Newauth realm="apps", type=1,
title="Login to \"apps\"", Basic realm="simple"
</pre> <p>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".
<h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;<a id="authentication.scheme.registration" href="#authentication.scheme.registration">Authenticaton Scheme Registry</a></h2>
<p id="rfc.section.5.1.p.1">The registration procedure for HTTP Authentication Schemes is defined by <a href="#authentication.scheme.registry" title="Authentication Scheme Registry">Section&nbsp;2.3</a> of this document.
<p id="rfc.section.5.1.p.2">The HTTP Method Authentication Scheme shall be created at &lt;<a href="http://www.iana.org/assignments/http-authschemes">http://www.iana.org/assignments/http-authschemes</a>&gt;.
<h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;<a id="status.code.registration" href="#status.code.registration">Status Code Registration</a></h2>
<p id="rfc.section.5.2.p.1">The HTTP Status Code Registry located at &lt;<a href="http://www.iana.org/assignments/http-status-codes">http://www.iana.org/assignments/http-status-codes</a>&gt; shall be updated with the registrations below:
<td class="left">401</td>
<td class="left">Unauthorized</td>
<td class="left"> <a href="#status.401" id="rfc.xref.status.401.1" title="401 Unauthorized">Section&nbsp;3.1</a>
<td class="left">407</td>
<td class="left">Proxy Authentication Required</td>
<td class="left"> <a href="#status.407" id="rfc.xref.status.407.1" title="407 Proxy Authentication Required">Section&nbsp;3.2</a>
<td class="left">Authorization</td>
<td class="left"> <a href="#header.authorization" id="rfc.xref.header.authorization.3" title="Authorization">Section&nbsp;4.1</a>
<td class="left">Proxy-Authenticate</td>
<td class="left"> <a href="#header.proxy-authenticate" id="rfc.xref.header.proxy-authenticate.2" title="Proxy-Authenticate">Section&nbsp;4.2</a>
<td class="left">Proxy-Authorization</td>
<td class="left"> <a href="#header.proxy-authorization" id="rfc.xref.header.proxy-authorization.2" title="Proxy-Authorization">Section&nbsp;4.3</a>
<td class="left">WWW-Authenticate</td>
<td class="left"> <a href="#header.www-authenticate" id="rfc.xref.header.www-authenticate.2" title="WWW-Authenticate">Section&nbsp;4.4</a>
<li>Applications which 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.
<p id="rfc.section.7.p.2">See <a href="p1-messaging.html#acks" title="Acknowledgments">Section 11</a> of <a href="#Part1" id="rfc.xref.Part1.12"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> for the Acknowledgments related to this document revision.
<td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-latest">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p1-messaging-latest (work in progress), February&nbsp;2012.
<td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, <a href="mailto:mnot@mnot.net" title="Rackspace">Nottingham, M., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-latest">HTTP/1.1, part 6: Caching</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p6-cache-latest (work in progress), February&nbsp;2012.
<td class="top"><a href="mailto:john@math.nwu.edu" title="Northwestern University, Department of Mathematics">Franks, J.</a>, <a href="mailto:pbaker@verisign.com" title="Verisign Inc.">Hallam-Baker, P.</a>, <a href="mailto:jeff@AbiSource.com" title="AbiSource, Inc.">Hostetler, J.</a>, <a href="mailto:lawrence@agranat.com" title="Agranat Systems, Inc.">Lawrence, S.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, Luotonen, A., and <a href="mailto:stewart@OpenMarket.com" title="Open Market, Inc.">L. Stewart</a>, “<a href="http://tools.ietf.org/html/rfc2617">HTTP Authentication: Basic and Digest Access Authentication</a>”, RFC&nbsp;2617, June&nbsp;1999.
<td class="reference"><b id="RFC4648">[RFC4648]</b></td>
<td class="top">Josefsson, S., “<a href="http://tools.ietf.org/html/rfc4648">The Base16, Base32, and Base64 Data Encodings</a>”, RFC&nbsp;4648, October&nbsp;2006.
<h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a>&nbsp;<a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFCs 2616 and 2617</a></h1>
<p id="rfc.section.A.p.1">The "realm" parameter isn't required anymore in general; consequently, the ABNF allows challenges without any auth parameters.
(<a href="#access.authentication.framework" title="Access Authentication Framework">Section&nbsp;2</a>)
<p id="rfc.section.A.p.2">The "b64token" alternative to auth-param lists has been added for consistency with legacy authentication schemes such as "Basic".
<p id="rfc.section.A.p.3">Change ABNF productions for header fields to only define the field value. (<a href="#header.field.definitions" title="Header Field Definitions">Section&nbsp;4</a>)
<div id="rfc.figure.u.10"></div> <pre class="inline"><a href="#header.authorization" class="smpl">Authorization</a> = credentials
<a href="#core.rules" class="smpl">BWS</a> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
<a href="#header.proxy-authenticate" class="smpl">Proxy-Authenticate</a> = *( "," OWS ) challenge *( OWS "," [ OWS
<a href="#header.proxy-authorization" class="smpl">Proxy-Authorization</a> = credentials
<a href="#header.www-authenticate" class="smpl">WWW-Authenticate</a> = *( "," OWS ) challenge *( OWS "," [ OWS challenge
<a href="#challenge.and.response" class="smpl">auth-param</a> = token BWS "=" BWS ( token / quoted-string )
<a href="#challenge.and.response" class="smpl">auth-scheme</a> = token
<a href="#challenge.and.response" class="smpl">b64token</a> = 1*( ALPHA / DIGIT / "-" / "." / "_" / "~" / "+" / "/" )
<a href="#challenge.and.response" class="smpl">challenge</a> = auth-scheme [ 1*SP ( b64token / [ ( "," / auth-param ) *(
<a href="#challenge.and.response" class="smpl">credentials</a> = auth-scheme [ 1*SP ( b64token / [ ( "," / auth-param )
<a href="#core.rules" class="smpl">quoted-string</a> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
</pre> <div id="rfc.figure.u.11"></div>
<p>ABNF diagnostics:</p><pre class="inline">; Authorization defined but not used
<h2 id="rfc.section.C.2"><a href="#rfc.section.C.2">C.2</a>&nbsp;Since draft-ietf-httpbis-p7-auth-00
<h2 id="rfc.section.C.3"><a href="#rfc.section.C.3">C.3</a>&nbsp;Since draft-ietf-httpbis-p7-auth-01
<h2 id="rfc.section.C.4"><a href="#rfc.section.C.4">C.4</a>&nbsp;<a id="changes.since.02" href="#changes.since.02">Since draft-ietf-httpbis-p7-auth-02</a></h2>
<h2 id="rfc.section.C.5"><a href="#rfc.section.C.5">C.5</a>&nbsp;<a id="changes.since.03" href="#changes.since.03">Since draft-ietf-httpbis-p7-auth-03</a></h2>
<p id="rfc.section.C.5.p.1">None.</p>
<h2 id="rfc.section.C.6"><a href="#rfc.section.C.6">C.6</a>&nbsp;<a id="changes.since.04" href="#changes.since.04">Since draft-ietf-httpbis-p7-auth-04</a></h2>
<h2 id="rfc.section.C.7"><a href="#rfc.section.C.7">C.7</a>&nbsp;<a id="changes.since.05" href="#changes.since.05">Since draft-ietf-httpbis-p7-auth-05</a></h2>
<h2 id="rfc.section.C.8"><a href="#rfc.section.C.8">C.8</a>&nbsp;<a id="changes.since.06" href="#changes.since.06">Since draft-ietf-httpbis-p7-auth-06</a></h2>
<p id="rfc.section.C.8.p.1">None.</p>
<h2 id="rfc.section.C.9"><a href="#rfc.section.C.9">C.9</a>&nbsp;<a id="changes.since.07" href="#changes.since.07">Since draft-ietf-httpbis-p7-auth-07</a></h2>
<h2 id="rfc.section.C.10"><a href="#rfc.section.C.10">C.10</a>&nbsp;<a id="changes.since.08" href="#changes.since.08">Since draft-ietf-httpbis-p7-auth-08</a></h2>
<h2 id="rfc.section.C.11"><a href="#rfc.section.C.11">C.11</a>&nbsp;<a id="changes.since.09" href="#changes.since.09">Since draft-ietf-httpbis-p7-auth-09</a></h2>
<p id="rfc.section.C.11.p.1">Partly resolved issues: </p>
<h2 id="rfc.section.C.12"><a href="#rfc.section.C.12">C.12</a>&nbsp;<a id="changes.since.10" href="#changes.since.10">Since draft-ietf-httpbis-p7-auth-10</a></h2>
<p id="rfc.section.C.12.p.1">None.</p>
<h2 id="rfc.section.C.13"><a href="#rfc.section.C.13">C.13</a>&nbsp;<a id="changes.since.11" href="#changes.since.11">Since draft-ietf-httpbis-p7-auth-11</a></h2>
<li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/130">http://tools.ietf.org/wg/httpbis/trac/ticket/130</a>&gt;: "introduction to part 7 is work-in-progress"
<li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/195">http://tools.ietf.org/wg/httpbis/trac/ticket/195</a>&gt;: "auth-param syntax"
<li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/237">http://tools.ietf.org/wg/httpbis/trac/ticket/237</a>&gt;: "absorbing the auth framework from 2617"
<p id="rfc.section.C.13.p.2">Partly resolved issues: </p>
<li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/141">http://tools.ietf.org/wg/httpbis/trac/ticket/141</a>&gt;: "should we have an auth scheme registry"
<h2 id="rfc.section.C.14"><a href="#rfc.section.C.14">C.14</a>&nbsp;<a id="changes.since.12" href="#changes.since.12">Since draft-ietf-httpbis-p7-auth-12</a></h2>
<p id="rfc.section.C.14.p.1">None.</p>
<h2 id="rfc.section.C.15"><a href="#rfc.section.C.15">C.15</a>&nbsp;<a id="changes.since.13" href="#changes.since.13">Since draft-ietf-httpbis-p7-auth-13</a></h2>
<h2 id="rfc.section.C.16"><a href="#rfc.section.C.16">C.16</a>&nbsp;<a id="changes.since.14" href="#changes.since.14">Since draft-ietf-httpbis-p7-auth-14</a></h2>
<h2 id="rfc.section.C.17"><a href="#rfc.section.C.17">C.17</a>&nbsp;<a id="changes.since.15" href="#changes.since.15">Since draft-ietf-httpbis-p7-auth-15</a></h2>
<li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/78">http://tools.ietf.org/wg/httpbis/trac/ticket/78</a>&gt;: "Relationship between 401, Authorization and WWW-Authenticate"
<li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/177">http://tools.ietf.org/wg/httpbis/trac/ticket/177</a>&gt;: "Realm required on challenges"
<li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/257">http://tools.ietf.org/wg/httpbis/trac/ticket/257</a>&gt;: "Considerations for new authentications schemes"
<li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/287">http://tools.ietf.org/wg/httpbis/trac/ticket/287</a>&gt;: "LWS in auth-param ABNF"
<li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/309">http://tools.ietf.org/wg/httpbis/trac/ticket/309</a>&gt;: "credentials ABNF missing SP (still using implied LWS?)"
<h2 id="rfc.section.C.18"><a href="#rfc.section.C.18">C.18</a>&nbsp;<a id="changes.since.16" href="#changes.since.16">Since draft-ietf-httpbis-p7-auth-16</a></h2>
<li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/320">http://tools.ietf.org/wg/httpbis/trac/ticket/320</a>&gt;: "add advice on defining auth scheme parameters"
<h2 id="rfc.section.C.19"><a href="#rfc.section.C.19">C.19</a>&nbsp;<a id="changes.since.17" href="#changes.since.17">Since draft-ietf-httpbis-p7-auth-17</a></h2>
<li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/314">http://tools.ietf.org/wg/httpbis/trac/ticket/314</a>&gt;: "allow unquoted realm parameters"
<li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/321">http://tools.ietf.org/wg/httpbis/trac/ticket/321</a>&gt;: "Repeating auth-params"
<h2 id="rfc.section.C.20"><a href="#rfc.section.C.20">C.20</a>&nbsp;<a id="changes.since.18" href="#changes.since.18">Since draft-ietf-httpbis-p7-auth-18</a></h2>
<p class="noprint"><a href="#rfc.index.4">4</a> <a href="#rfc.index.A">A</a> <a href="#rfc.index.B">B</a> <a href="#rfc.index.C">C</a> <a href="#rfc.index.G">G</a> <a href="#rfc.index.H">H</a> <a href="#rfc.index.P">P</a> <a href="#rfc.index.R">R</a> <a href="#rfc.index.S">S</a> <a href="#rfc.index.W">W</a>
<li>401 Unauthorized (status code)&nbsp;&nbsp;<a href="#rfc.iref.12"><b>3.1</b></a>, <a href="#rfc.xref.status.401.1">5.2</a></li>
<li>407 Proxy Authentication Required (status code)&nbsp;&nbsp;<a href="#rfc.iref.13"><b>3.2</b></a>, <a href="#rfc.xref.status.407.1">5.2</a></li>
<li><tt>auth-param</tt>&nbsp;&nbsp;<a href="#rfc.iref.a.2"><b>2.1</b></a></li>
<li><tt>auth-scheme</tt>&nbsp;&nbsp;<a href="#rfc.iref.a.1"><b>2.1</b></a></li>
<li>Authorization header field&nbsp;&nbsp;<a href="#rfc.xref.header.authorization.1">2.1</a>, <a href="#rfc.xref.header.authorization.2">3.1</a>, <a href="#rfc.iref.a.3"><b>4.1</b></a>, <a href="#rfc.xref.header.authorization.3">5.3</a></li>
<li><tt>b64token</tt>&nbsp;&nbsp;<a href="#rfc.iref.b.1"><b>2.1</b></a></li>
<li><tt>challenge</tt>&nbsp;&nbsp;<a href="#rfc.iref.c.1"><b>2.1</b></a></li>
<li><tt>credentials</tt>&nbsp;&nbsp;<a href="#rfc.iref.c.2"><b>2.1</b></a></li>
<li><tt>auth-param</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>2.1</b></a></li>
<li><tt>auth-scheme</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.1"><b>2.1</b></a></li>
<li><tt>Authorization</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.6"><b>4.1</b></a></li>
<li><tt>b64token</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>2.1</b></a></li>
<li><tt>challenge</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>2.1</b></a></li>
<li><tt>credentials</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.5"><b>2.1</b></a></li>
<li><tt>Proxy-Authenticate</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.7"><b>4.2</b></a></li>
<li><tt>Proxy-Authorization</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.8"><b>4.3</b></a></li>
<li><tt>WWW-Authenticate</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.9"><b>4.4</b></a></li>
<li>Authorization&nbsp;&nbsp;<a href="#rfc.xref.header.authorization.1">2.1</a>, <a href="#rfc.xref.header.authorization.2">3.1</a>, <a href="#rfc.iref.h.1"><b>4.1</b></a>, <a href="#rfc.xref.header.authorization.3">5.3</a></li>
<li>Proxy-Authenticate&nbsp;&nbsp;<a href="#rfc.xref.header.proxy-authenticate.1">3.2</a>, <a href="#rfc.iref.h.2"><b>4.2</b></a>, <a href="#rfc.xref.header.proxy-authenticate.2">5.3</a></li>
<li>Proxy-Authorization&nbsp;&nbsp;<a href="#rfc.xref.header.proxy-authorization.1">3.2</a>, <a href="#rfc.iref.h.3"><b>4.3</b></a>, <a href="#rfc.xref.header.proxy-authorization.2">5.3</a></li>
<li>WWW-Authenticate&nbsp;&nbsp;<a href="#rfc.xref.header.www-authenticate.1">3.1</a>, <a href="#rfc.iref.h.4"><b>4.4</b></a>, <a href="#rfc.xref.header.www-authenticate.2">5.3</a></li>
<li><em>Part1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.1</a>, <a href="#rfc.xref.Part1.2">1.2</a>, <a href="#rfc.xref.Part1.3">1.2.1</a>, <a href="#rfc.xref.Part1.4">1.2.1</a>, <a href="#rfc.xref.Part1.5">1.2.1</a>, <a href="#rfc.xref.Part1.6">1.2.1</a>, <a href="#rfc.xref.Part1.7">1.2.1</a>, <a href="#rfc.xref.Part1.8">2.2</a>, <a href="#rfc.xref.Part1.9">2.3.1</a>, <a href="#rfc.xref.Part1.10">4.2</a>, <a href="#rfc.xref.Part1.11">4.4</a>, <a href="#rfc.xref.Part1.12">7</a>, <a href="#Part1"><b>8.1</b></a><ul>
<li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.9">2.3.1</a></li>
<li><em>Section 3.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.4">1.2.1</a>, <a href="#rfc.xref.Part1.5">1.2.1</a></li>
<li><em>Section 3.2.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.6">1.2.1</a>, <a href="#rfc.xref.Part1.7">1.2.1</a></li>
<li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.8">2.2</a>, <a href="#rfc.xref.Part1.10">4.2</a>, <a href="#rfc.xref.Part1.11">4.4</a></li>
<li><em>Section 11</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.12">7</a></li>
<li><em>Part6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.1">4.1</a>, <a href="#Part6"><b>8.1</b></a><ul>
<li><em>Section 1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.1">4.1</a></li>
<li>Protection Space&nbsp;&nbsp;<a href="#rfc.iref.p.1">2.2</a></li>
<li>Proxy-Authenticate header field&nbsp;&nbsp;<a href="#rfc.xref.header.proxy-authenticate.1">3.2</a>, <a href="#rfc.iref.p.2"><b>4.2</b></a>, <a href="#rfc.xref.header.proxy-authenticate.2">5.3</a></li>
<li>Proxy-Authorization header field&nbsp;&nbsp;<a href="#rfc.xref.header.proxy-authorization.1">3.2</a>, <a href="#rfc.iref.p.3"><b>4.3</b></a>, <a href="#rfc.xref.header.proxy-authorization.2">5.3</a></li>
<li>Realm&nbsp;&nbsp;<a href="#rfc.iref.r.1">2.2</a></li>
<li><em>RFC3986</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.1">2.1</a>, <a href="#RFC3986"><b>8.2</b></a></li>
<li><em>RFC4648</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4648.1">2.1</a>, <a href="#RFC4648"><b>8.2</b></a></li>
<li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">2.3</a></li>
<li>401 Unauthorized&nbsp;&nbsp;<a href="#rfc.iref.s.1"><b>3.1</b></a>, <a href="#rfc.xref.status.401.1">5.2</a></li>
<li>407 Proxy Authentication Required&nbsp;&nbsp;<a href="#rfc.iref.s.2"><b>3.2</b></a>, <a href="#rfc.xref.status.407.1">5.2</a></li>
<li>WWW-Authenticate header field&nbsp;&nbsp;<a href="#rfc.xref.header.www-authenticate.1">3.1</a>, <a href="#rfc.iref.w.1"><b>4.4</b></a>, <a href="#rfc.xref.header.www-authenticate.2">5.3</a></li>