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Versions: 00 01 02

Internet Engineering Task Force                         N. Williams, Ed.
Internet-Draft                                         Cryptonector, LLC
Intended status: Standards Track                           April 8, 2020
Expires: October 10, 2020


     Accept-Auth HTTP Header for 3xx/401 Negotiation, and Redirect
                         Authentication Scheme
            draft-williams-http-accept-auth-and-redirect-02

Abstract

   The Hyper-Text Transport Protocol (HTTP) offers several
   authentication schemes, but many sites use redirection-based
   protocols to authenticate users.  Some servers are faced with a
   connundrum, having to choose between two mutually-exclusive options:
   redirect responses or 401 (authentication required) responses without
   knowing which the user-agent is most likely to support.

   This document specifies new HTTP request headers by which many
   applications can improve interoperability even without changing their
   HTTP implementations.  These new headers allow user-agents to
   advertise authentication- and redirect-related capbilities that
   servers can use to better make authentication and/or redirect
   decisions.

   Also specified is a new HTTP authentication scheme named "Redirect"
   that enables communication between redirecting and redirected
   authorities via preservation of "Authorization" headers across
   redirections.  This enables arbitrary authentication and
   authorization protocols to work without requiring user-agent support
   for them and without having to (ab)use URI query parameters.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."




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   This Internet-Draft will expire on October 10, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   1.1.  Requirements Language . . . . . . . . . . . . . . . . . . .   3
   2.  Accept-Redirect and       Accept-Redirect-Auth  . . . . . . .   3
   3.  Accept-Auth . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  The Redirect Authentication Scheme  . . . . . . . . . . . . .   4
   4.1.  Redirect Examples . . . . . . . . . . . . . . . . . . . . .   7
   5.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.1.  Applicability of Accept-* Headers . . . . . . . . . . . . .   8
   5.2.  Applicability of Redirect Auth Scheme . . . . . . . . . . .   8
   6.  Mixing Redirection and Authentication Requests  . . . . . . .   9
   6.1.  3xx Responses with WWW-Authenticate . . . . . . . . . . . .   9
   6.2.  401 Responses with Location . . . . . . . . . . . . . . . .  10
   7.  Auth-params for Selected Authentication Mechanisms  . . . . .  10
   8.  Server-Side Selection of Authentication Schemes . . . . . . .  10
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  11
   11.1.  Security Considerations for the Redirect Auth Scheme . . .  11
   11.2.  Multi-Level Negotiation  . . . . . . . . . . . . . . . . .  12
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
   12.1.  Normative References . . . . . . . . . . . . . . . . . . .  13
   12.2.  Informative References . . . . . . . . . . . . . . . . . .  14
   12.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14








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1.  Introduction

   The Hyper-Text Transport Protocol (HTTP) RFC7230 [RFC7230] provides
   several schemes for user authentication.  There also are popular ways
   of authenticating users based on redirection rather than standard
   HTTP authentication schemes.  Heretofore, HTTP has provided no
   standard way for servers to know which authentication schemes,
   including redirect-based methods, a given user-agent supports, but
   servers must choose between either redirection or HTTP
   authentication, and these two are mutually exclusive.

   This situation arises especially in corporate networks where JSON Web
   Tokens (JWT) [RFC7519] and Negotiate [RFC4559] are both used, the
   latter usually with the Kerberos [RFC4120] GSS-API [RFC2743]
   mechanism [RFC4121].

   We address this problem by adding new request headers, "Accept-
   Auth:", "Accept-Redirect-Auth:", and "Accept-Redirect:" by which a
   user-agent can indicate which HTTP authentication schemes, if any, it
   supports, including redirection.

1.1.  Requirements Language

   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 RFC 2119 [RFC2119].

2.  Accept-Redirect and Accept-Redirect-Auth

   The Accept-Redirect request header has two possible values: "yes" and
   "no".  If "yes", this means the user-agent will follow redirections,
   and the user-agent may or may not be willing to authenticate at the
   redirected origin depending on local policy.

   The Accept-Redirect-Auth request header exists to indicate which
   authorities the user-agent is willing to redirect to and authenticate
   at.  Its value is a whitespace-separate list of domainnames.  If
   empty or has just the value ".", then the service can conclude only
   that the user-agent has a whitelist, but is not disclosing it.

3.  Accept-Auth

   The Accept-Auth request header may have multiple values, or be
   present multiple times, as with most HTTP headers.  Each value names
   one authentication schemes, and optionally may indicate schemes-
   specific metadata.





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   Accept-Auth values are similar to WWW-Authenticate values [RFC7235],
   but they do not have quite the same form, and they are not
   challenges.  Using ABNF [RFC5234]:

   ; Can we use the RFC7230 #rule ABNF extension here?
   Accept-Auth-values = Accept-Auth-value *( OWS ","
                                             OWS Accept-Auth-value )
   Accept-Auth-value = auth-scheme [1*SP
                                    ( auth-param *( "+" auth-param ) ]
   auth-scheme = token
   auth-param = token BWS "=" BWS ( token / quoted-string )
   token          = 1*tchar
   tchar          = "!" / "'" / "*" / "-" / "." / "^"
                  / "_" / "`" / "|" / "~" / DIGIT / ALPHA
                  ; any VCHAR, except delimiters; here we use "+"
                  ; as a delimiter, so our token definition is
                  ; different from RFC7230's.

   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>

                          Accept-Auth value ABNF.

                                 Figure 1

4.  The Redirect Authentication Scheme

   Many sites use redirect-based protocols for authentication.  Such
   protocols exchange cryptographic messages between a relying party
   origin and an authenticator origin.  Some such protocols use URI
   query parameters to carry cryptographic messages.  Others depend on
   the browser HTML and ECMAScript ecosystem, using a script to run HTTP
   requests from the authenticator to the relying party with a token in
   Authorization request header.  In the latter case, the server
   exchanges the token for a cookie, and a script on the authenticator
   page then effects a redirect by changing the window location.

   Such redirect-based protocols do not work for non-browser user-
   agents.

   [[COMMENT_CB0: It might be good to also specify request headers for
   redirected requests that user-agents can use for passing channel
   binding information to auth services.  E.g., Authorization-Channel-
   Binding: <type> <cb-data>.  This would allow Authorization tokens to
   be channel-bound.  Of course, there are difficulties here that would
   require additional thinking.  For example, using unique CB would
   require that the user-agent keep a connection open to the redirecting



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   origin.  While end-point CB would fail if multiple servers serve the
   same origin using different server certificates for the same names.
   Binding to the dNSName and the issuer, however, would work, but that
   would be a new CB type and would require registration in the IANA CB
   type registry.  CB support could always be added later.  --NW]]
   [[COMMENT_CB1: Possible new CB types include: dNSName+hash(issuer-
   cert/SPKI), some sort of TLS session ID possibly constructed using
   the TLS key material exporter but derived in such a way that it
   identifies a set of connections resumed from the same original
   handshake.  The latter would be prone to failure on resumption if the
   resumption ticket is rejected for any reason, but otherwise would
   work really well for tokbind-style token protocols, especially for
   user-agents that can retry.  --NW]]

   User-agents normally do not copy response headers from redirect
   responses redirected requests.  One common non-browser user-agent,
   the PowerShell command-line user-agent [1], has an option,
   "-PreserveAuthorizationOnRedirect" that causes it to copy
   Authorization headers from redirect responses to redirected requests.
   This enables some redirect-based workflows to work even though that
   user-agent is not a browser, lacks interaction capabilities, HTML
   rendering, or JavaScript support.

   Here we define the "Redirect" HTTP authentication scheme.  This
   scheme lets arbitrary authentication (and authorization) protocols
   exchange cryptographic messages between the relying party origin and
   the authenticator origin over headers rather than URI parameters.
   This is done by copying ("preserving") any "Authorization" headers in
   a redirect response to the redirected request.

   For our purposes, a "redirect response" is either a 3xx redirect
   response with a Location header, or a 401 response with a WWW-
   Authenticate header naming the Redirect authentication scheme and a
   Location header.

   o  User-agents that support the Redirect HTTP authentication scheme
      MUST recognize a 401 Redirect challenge as a redirect response.

         [[COMMENT_0: QUESTION: What, if anything, should we say about
         the method used by the user-agent when chasing a redirection?
         --NW]]

         [[COMMENT_1: One possibility is to let the redirecting origin
         specify the method and state some constraints (e.g., if the
         original method cannot have a request body, then the next
         method must be GET, else ???).  --NW]]





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         [[COMMENT_2: Since the intent is to authenticate the user, a
         GET should always be good enough.  In particular, the
         authenticator origin may not need to see the original request
         body at all, though it may need to know the original method,
         and it can get that from the relying party (e.g., via the
         Redirect header preservation mechanism).  --NW]]

   o  User-agents SHOULD also consider challenges for other
      authentication schemes offered by the server.  E.g., if the server
      offers a Negotiate [RFC4559] challenge and a Redirect challenge,
      the user-agent may choose either (or neither) of the two.

   o  Unless rejected by local policy (or the user), user-agents that
      support the Redirect HTTP authentication scheme MUST copy any
      Authorization headers in redirect responses to the redirected
      request.

   o  Servers needing to authenticate the user when the user-agent has
      advertised support for the Redirect authentication scheme SHOULD
      respond with a 401 with a "challenge" for the Redirect
      authentication scheme and a Location header, and MAY include an
      Authorization header in the response that the user-agent then MUST
      copy to the redirected request if it chooses to follow the
      redirection.  Servers MAY use a 3xx response instead.

   o  Servers that have been redirected to MUST apply local policy to
      decide:

      *  whether to accept redirections from the redirecting origin
         (identified by the Referer header or by a cryptographic token
         in the preserved Authorization header);

      *  whether to further redirect the request (as usual) and whether
         to set an Authorization header in the redirect response;

      *  whether to authenticate the user (as usual);

      *  whether to redirect back to the redirecting origin, and whether
         to set an Authorization header in the redirect response.

   o  User-agents may consult the user (if interactive), and/or a local
      policy (e.g., a white-list of acceptable origins for
      redirections), in order to decide whether to follow the
      redirection.

   o  Note that the redirected-to service should always have enough
      information to decide whether to accept or reject a redirection




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      (e.g., via the Referer header), and MUST have and apply local
      policy of its own.

   Note that nothing in this document alters or obviates Cross-Origin
   Resource Sharing policy and considerations.

4.1.  Redirect Examples

   Consider a URL https://janedoe.catvidhub.com.example/v0.mpg which
   permanently redirects to https://janedoe.catvidhub.io.example/v0.mpg,
   and suppose the latter also wants to authenticate users via
   redirection to an authenticator at
   https://auth.catvidhub.nu.example/.  Let us label these A, B, and C
   respectively.

   The first redirection in this example is not involved in
   authentication, and is included only to show that a redirection chain
   where only parts of it are involved in authentication is possible.

   In this example we should see a normal redirect from A to B, and at B
   we should see a redirect to C, and then finally a redirect back from
   C to B, and then B should serve the desired resource ("/v0.mpg") if C
   provided the user-agent with a suitable token.  Using the Redirect
   auth scheme we should see:

   o  Server A would respond with a normal 3xx redirect to B, not a 401
      authenticate-with-Redirect, and no Authorization headers in the
      redirect response.

   o  Server B would respond with a 401 authenticate-with-Redirect
      response and (possibly) a Authorization header in the response by
      which it might send a signed request for authorization to the
      "/v0.mpg" resource.

   o  Server C would check any Authorization headers in the request and
      possibly authenticate the user-agent somehow (e.g., using any
      cookies sent by the user-agent, using client certificates in TLS,
      by responding with a 401 for the user-agent to authenticate using
      some HTTP scheme, a further Redirect or plain redirection, or by
      interacting with the user if the user-agent is a browser).

   o  Once the user is authenticated, server C would check the user's
      authorization to access the resource ("/v0.mpg"), and if
      permitted, would respond with a 3xx response with an Authorization
      header bearing a cryptographic token for B attesting to the user's
      authorization.





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   o  Finally, on the redirect back to B, the user-agent would preserve
      the Authorization header from the response from C, which means
      server B would see it, verify its integrity, decode it, and -if
      the token grants access- then serve the resource.

5.  Applicability

   Two different and only somewhat related features are specified here.
   One is intended to help interoperability in heterogeneous
   environments with minimal or no changes to existing HTTP
   implementations, just changes to applications.  The other is intended
   to perfect existing redirect-based authentication and authorization
   protocols.

5.1.  Applicability of Accept-* Headers

   The purpose of the Accept-Auth Section 3, Accept-Redirect Section 2,
   and Accept-Redirect-Auth Section 2 request headers is to improve
   interoperability in heterogeneous environments with minimal or no
   changes to HTTP implementations.

   For example, an application could set these request headers on
   requests without changes to the user-agent.  That's because setting
   arbitrary request headers is a common feature of HTTP user-agent
   implementations.

   It is also common for HTTP server implementations to allow
   applications to inspect request headers produce 3xx redirect or 401
   responses.

   Thus one can modify client applications to set these headers, and
   server applications to check them and choose between 3xx redirect and
   401 authenticate options, as well as between authentication schemes,
   based on the presence of those headers.  All without changes to HTTP
   implementations.

   HTTP implementors will probably want to add support for these headers
   directly, but that isn't necessary in order to improve
   interoperability.

5.2.  Applicability of Redirect Auth Scheme

   The new HTTP auth scheme, Redirect Section 4 also can be implemented
   without changes to HTTP implementations, but will be much more useful
   if implemented at least by user-agents.

   In the short-term, the HTTP auth scheme, Redirect, is not applicable
   to any existing protocols or applications.  However, existing



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   authentication and authorization systems, such as various Security
   Assertion Markup Language (SAML) profiles, as well as OpenID Connect
   (OIDC) and OAuth 2.0 [RFC6749] mechanisms in general, such as JWT
   [RFC7519], can be adapted to use Redirect.  [[COMMENT_REFS_NEEDED0:
   Need to add references for SAML.  Bibxml does not have any entries
   for OASIS specs! --NW]]

   Specifically, it is better to use headers for communication between
   relying parties and auth services than it is to use URI query
   parameters, as the latter imposes on application designers.  Besides
   this, the Redirect auth scheme can greatly simplify adding support
   for, e.g., JWT, even for non-browser applications.

   Thus the Redirect HTTP auth scheme is more likely to be useful in the
   future.  Note though that given user-agent support for Redirect, it's
   fairly easy to adapt SAML/OIDC/JWT identity providers to use it.

6.  Mixing Redirection and Authentication Requests

   Making use of the new Accept-Auth, Accept-Redirect, and Accept-
   Redirect-Auth request headers will often require no changes to
   existing HTTP user-agents and servers.  This is because the
   application usually gets to set and inspect arbitrary headers.  On
   the server side it may be difficult for an application to add support
   for the Redirect authentication scheme without modifying the HTTP
   server.  Therefore it may be difficult for an application to issue a
   401 Redirect, and it may have to use a 3xx redirect instead.

   Therefore, user-agents MUST treat 3xx and 401 Redirect responses
   similarly, applying the same local policy in either case.

6.1.  3xx Responses with WWW-Authenticate

   If a server responds with a 3xx and includes not only a Location
   header but also a WWW-Authenticate header, then the redirect denotes
   intent to authenticate the user.  In this case, the user-agent SHALL
   consider the response to be either a redirect or a request to
   authenticate, at the user-agent's choice.  The HTTP method to use at
   the new Location SHALL be as specified for the status code used by
   the server.

   Note that many user-agents will not understand that such responses
   represent an option to authenticate with some authentication scheme.








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6.2.  401 Responses with Location

   If a server responds with a 401 and includes not just a WWW-
   Authenticate header but also a Location header, then the Location
   header's presence denotes the intent to authenticate the user either
   via the server's authentication scheme offerings, or redirection.  In
   this case, a user-agent conforming to this specification SHALL
   consider the response to be either a redirect or a request to
   authenticate, at the user-agent's choice, and SHOULD pick and execute
   one of those two options.  The user-agent SHOULD use the GET method
   at the new Location, with the expectation of eventually being
   redirected back to the original URI authority, at which point the
   user-agent, if it chooses to retry the original request, SHOULD use
   the original method.

   Note that many user-agents will not understand that such responses
   represent an option to chase a redirection.

7.  Auth-params for Selected Authentication Mechanisms

   We specify here a few OPTIONAL parameters for existing HTTP
   authentication schemes that user-agents may use to convey relevant
   information to a server.

   o  For the Basic [RFC2617] authentication mechanism, user-agents MAY
      include a "realm" parameter.

   o  For the Digest [RFC2617] authentication mechanism, user-agents MAY
      include "realm", "domain", "algorithm", and "qop-options"
      parameters.

   o  For the Negotiate [RFC4559] authentication mechanism, user-agents
      MAY include a "mechs" auth-param whose value is a whitespace-
      separate list of Object IDentifiers (OIDs) in dotted number
      notation.

   o  For the Redirect authentication mechanism defined here, we define
      an auth-param, "auth-svcs" whose value is a list of whitespace-
      separated domainnames that the user-agent will follow redirections
      to.

8.  Server-Side Selection of Authentication Schemes

   Servers that support only one authentication scheme have no
   difficulty choosing which scheme to use.  For other servers, when the
   user-agent does not include the Accept-Auth header in its request, we
   have no advice.  When a server supports multiple authentication
   schemes and the user-agent does include the Accept-Auth header in its



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   request, then the server SHOULD select at least one scheme for a 401
   response's WWW-Authenticate header that the user-agent also supports,
   but the server MAY respond with a 3xx redirect response if the user-
   agent indicated support for redirects via the Accept-Redirect header
   or by advertising support for the Redirect HTTP authentication
   scheme.

9.  Acknowledgements

   Ben Kaduk, Simo Sorce, Viktor Dukhovni, Bill Bernsen, Andrew Brown,
   and Geoffrey Thomas provided feedback and some review.

10.  IANA Considerations

   IANA is requested to assign an expert to run the Expert Review for
   the registration of the Accept-Auth, Accept-Redirect, and Accept-
   Redirect-Auth headers in the message header registry.

   Upon completion of IETF Review, IANA is directed to add the Redirect
   authentication scheme to the HTTP Authentication Scheme registry.

   There is no registry for auth-params for HTTP authentication schemes,
   nor do we request the creation of such a registry.  The auth-params
   used here bear some relation to those of the authentication schemes
   they are used with, but they are essentially a distinct namespace.
   Future additions of auth-params for use in the Accept-Auth header
   will have to update this document.

11.  Security Considerations

   The Accept-Auth header is security-relevant as it helps negotiate
   authentication, which is a positive consideration.  Negative security
   considerations include multi-level negotiation issues Section 11.2,
   as well as a privacy concern: that the Accept-Auth header may help
   fingerprint user-agents.

   Privacy-conscious user-agents SHOULD have local policy about which
   authorities to use the new Accept-Auth, Accept-Redirect, and Accept-
   Redirect-Auth headers.

11.1.  Security Considerations for the Redirect Auth Scheme

   The Authorization header preservation behavior allows attackers to
   convey malformed tokens to victim servers, allowing them to probe for
   parsing bugs.  However, this is already true for the URI itself,
   therefore this is not a new issue.





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   Open redirectors allow malicious redirects to sites that could set an
   Authorization header on a redirect back to the site with the open
   redirector.  This would allow an attacker to make a user thing they
   are logged in as themselves when they are instead logged in as the
   attacker, and then the victim user might get fooled into sending the
   attacker sensitive information.  This is not a new problem, as it is
   already a problem for auth systems, such as OIDC, that use URI query
   parameters to convey cryptographic tokens ("codes" in OIDC parlance).

   Open redirectors are a security vulnerability in general.  Servers
   MUST NOT implement open redirects.

   Adding support for channel / token binding to the Redirect HTTP auth
   scheme may well be possible and desirable.  This would consist of
   request headers set by the user-agent on redirected requests that
   would carry channel binding (CB) data for one or more CB types
   corresponding to the original origin (and/or previous hop).

   One concern is that servers could cause user-agents to engage in
   authentication schemes they shouldn't want to -- that is a
   possibility regardless of whether the user-agent advertises support
   for an authentication scheme or not.  As usual, local policy is
   relevant.  For example, the "curl" user-agent by default will not
   chase redirections, and if enabled, it will by default not
   authenticate at any redirected authority (this can be further
   enabled).  User-agents SHOULD have local policy about which
   redirections they will accept, whether to authenticate to redirected
   authorities, and with what methods.  For example, a user-agent may be
   willing to use the Negotiate [RFC4559] authentication scheme at some
   or any redirected authorities if it is happy to let Kerberos
   [RFC4121] implementations, including Key Distribution Centers (KDCs),
   apply policy on the user-agent's behalf, but may not be willing to
   perform Basic [RFC2617], Digest [RFC2617], or SCRAM [RFC7804]
   authentication to any redirected authorities not on a local
   whitelist.

11.2.  Multi-Level Negotiation

   One important security consideration of the Accept-Auth header is
   that it may lead to multiple levels of negotiation (e.g., via the
   Negotiate [RFC4559] authentication method).  Multi-level negotiations
   can fail to select to select a workable option, or may select a sub-
   optimal (e.g., less secure) option.

   For example, a user-agent might be able to use Digest authentication
   and Negotiate with some GSS-API [RFC2743] mechanism X, while the
   server might be able to use Digest and Negotiate with some GSS-API
   mechanism Y, and the server might prefer Y.  If the server knows only



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   that the user-agent supports Digest and Negotiate, but not that the
   user-agent does not support GSS-API mechanism Y, then the server may
   send a challenge to use Negotiate and then the whole negotiation will
   fail.

   In the above example the user-agent could recover by retrying without
   advertising Negotiate in its Accept-Auth header, but the user-agent
   is not likely to do this on account of that being too complex.
   Neither the user-agent nor the server are likely to detect and
   recover from sub-optimal selections.

   To avoid this failure more, user-agents SHOULD use auth-params to
   convey information that the server might need to make an appropriate
   selection.

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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, DOI 10.17487/RFC2617, June 1999,
              <https://www.rfc-editor.org/info/rfc2617>.

   [RFC4559]  Jaganathan, K., Zhu, L., and J. Brezak, "SPNEGO-based
              Kerberos and NTLM HTTP Authentication in Microsoft
              Windows", RFC 4559, DOI 10.17487/RFC4559, June 2006,
              <https://www.rfc-editor.org/info/rfc4559>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.







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   [RFC7235]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Authentication", RFC 7235,
              DOI 10.17487/RFC7235, June 2014,
              <https://www.rfc-editor.org/info/rfc7235>.

12.2.  Informative References

   [RFC2743]  Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743,
              DOI 10.17487/RFC2743, January 2000,
              <https://www.rfc-editor.org/info/rfc2743>.

   [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
              Kerberos Network Authentication Service (V5)", RFC 4120,
              DOI 10.17487/RFC4120, July 2005,
              <https://www.rfc-editor.org/info/rfc4120>.

   [RFC4121]  Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
              Version 5 Generic Security Service Application Program
              Interface (GSS-API) Mechanism: Version 2", RFC 4121,
              DOI 10.17487/RFC4121, July 2005,
              <https://www.rfc-editor.org/info/rfc4121>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <https://www.rfc-editor.org/info/rfc6749>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.

   [RFC7804]  Melnikov, A., "Salted Challenge Response HTTP
              Authentication Mechanism", RFC 7804, DOI 10.17487/RFC7804,
              March 2016, <https://www.rfc-editor.org/info/rfc7804>.

12.3.  URIs

   [1] https://docs.microsoft.com/en-
       us/powershell/module/microsoft.powershell.utility/invoke-
       webrequest?view=powershell-7

Author's Address









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   Nico Williams (editor)
   Cryptonector, LLC
   Austin, TX
   USA

   Email: nico@cryptonector.com













































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