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Versions: 00 01 02 03

Network Working Group                                        N. Williams
Internet-Draft                                              Cryptonector
Intended status: Informational                           August 15, 2012
Expires: February 16, 2013


  RESTful Authentication Pattern for the Hypertext Transport Protocol
                                 (HTTP)
                    draft-williams-http-rest-auth-03

Abstract

   This document proposes a "RESTful" pattern of authentication for
   HTTP/1.0, 1.1, and 2.0.  The goal is to make it easy to add
   authentication mechanisms to HTTP and to make it easy to implement
   them even without much help from the HTTP stack (though it is best to
   integrate authentication into the stack, of course).

   Among other benefits of RESTauth: it is orthogonal to "HTTP routers"
   and proxies, it results in session Uniform Resource Identifiers
   (URIs) that can be DELETEd to logout, naturally supports multi-legged
   authentication schemes, and it can be universally implemented on the
   server side with the Common Gateway Interface (CGI) and FastCGI.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 16, 2013.

Copyright Notice

   Copyright (c) 2012 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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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.












































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Table of Contents

   1.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  4
   2.      Conventions used in this document  . . . . . . . . . . . .  6
   3.      API-Imposed Constraints  . . . . . . . . . . . . . . . . .  7
   4.      Protocol . . . . . . . . . . . . . . . . . . . . . . . . .  8
   4.1.    Negotiable Parameters  . . . . . . . . . . . . . . . . . .  8
   4.1.1.  Strong Binding to TLS  . . . . . . . . . . . . . . . . . .  9
   4.1.2.  WWW-Authenticate Header Value Prefix Syntax  . . . . . . .  9
   4.1.3.  WWW-ChannelBinding-Types Header  . . . . . . . . . . . . .  9
   4.1.4.  WWW-ChannelBinding-Type Header . . . . . . . . . . . . . . 10
   4.1.5.  WWW-SessionBinding-Type Header . . . . . . . . . . . . . . 10
   4.1.6.  WWW-ReplayProtection Header  . . . . . . . . . . . . . . . 10
   4.2.    Protocol Flow  . . . . . . . . . . . . . . . . . . . . . . 10
   4.2.1.  One Round Trip Optimization: Challenges Born in
           WWW-Authenticate Headers . . . . . . . . . . . . . . . . . 11
   4.3.    Session Binding Types: Cookie, URI, and MAC  . . . . . . . 11
   4.3.1.  The New WWW-Session-URI Header . . . . . . . . . . . . . . 12
   4.3.2.  The New WWW-Session-MAC Header . . . . . . . . . . . . . . 12
   4.3.3.  A MAC Trailer??  . . . . . . . . . . . . . . . . . . . . . 12
   5.      HTTP "Routing" and Authentication  . . . . . . . . . . . . 13
   6.      In-band HTTP Authentication Alternatives . . . . . . . . . 14
   7.      Sample/Potential RESTauth Authentication Mechanisms  . . . 15
   7.1.    OAuth via RESTauth . . . . . . . . . . . . . . . . . . . . 15
   7.1.1.  OAuth 1.0  . . . . . . . . . . . . . . . . . . . . . . . . 15
   7.1.2.  OAuth 2.0  . . . . . . . . . . . . . . . . . . . . . . . . 15
   7.2.    Adapting SSHv2 Authentication Mechanisms to RESTauth . . . 15
   7.2.1.  RESTauth Mechanism Names for SSHv2 Userauth Methods  . . . 15
   7.2.2.  Nonces . . . . . . . . . . . . . . . . . . . . . . . . . . 16
   7.2.3.  "Session ID" . . . . . . . . . . . . . . . . . . . . . . . 16
   7.3.    Adapting IKEv2 Authentication Mechanisms to RESTauth . . . 16
   7.3.1.  Adapting IKEv2 Password Authenticated Connection
           Establishment (PACE) to RESTauth . . . . . . . . . . . . . 16
   7.4.    Using SASL Authentication Mechanisms with RESTauth . . . . 16
   7.4.1.  Using SCRAM in RESTauth  . . . . . . . . . . . . . . . . . 17
   7.4.2.  Using SCRAM with Round Trip Optimization in RESTauth . . . 18
   7.5.    Using GSS-API Authentication Mechanisms with RESTauth  . . 19
   8.      IANA Considerations  . . . . . . . . . . . . . . . . . . . 20
   9.      Security Considerations  . . . . . . . . . . . . . . . . . 21
   10.     TODO . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
   11.     References . . . . . . . . . . . . . . . . . . . . . . . . 23
   11.1.   Normative References . . . . . . . . . . . . . . . . . . . 23
   11.2.   Informative References . . . . . . . . . . . . . . . . . . 23
           Author's Address . . . . . . . . . . . . . . . . . . . . . 25







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1.  Introduction

   We propose a pattern for HTTP [RFC2616] [XXX add reference to
   HTTP/2.0 as well] authentication mechanisms that, by being "RESTful",
   obtains a number of benefits:

   o  authentication that works with all versions of HTTP, even when the
      authentication mechanism requires multiple round trips;

   o  compatibility with "HTTP routing" by making no assumptions that
      related requests are sent over the same TCP/TLS connection;

   o  a "session URI" results that can be used to multiplex multiple
      sessions onto the same TCP/TLS connections;

   o  a "session URI" results that can be DELETEd to effect logout;

   o  a "session URI" results that has better security semantics than
      HTTP cookies;

   o  the ability to refer to multiple sessions in one request wherever
      such a concept might be useful;

   o  can be implemented by any application without changes being
      required to any HTTP stack;

   o  can be implemented by the HTTP stack;

   o  on the server side this can be implemented entirely via CGI and
      FastCGI;

   o  by its RESTful nature, multi-legged authentication message
      exchanges are naturally handled without making any changes to
      HTTP.

   There are probably other benefits not listed above.

   The rough outline of the protocol is quite simple:

   1.  initial authentication messages are POSTed to an agreed-upon or
       indicated resource...

   2.  ....which then results in a new resource being created with the
       authentication reply message as the new resource's
       representation.

   3.  Thereafter any additional authentication message exchanges needed
       (for multi-legged mechanisms) are POSTed to the new resource



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       creating additional resources.

   4.  The resource created by the POSTing of the initial authentication
       mechanism identifies the resulting session, and its URI is known
       as the session URI.

   5.  Session URIs can be used to multiplex multiple sessions over the
       same TCP/TLS connections, implement logout, and share sessions
       across multiple related servers.

   Server-initiated authentication is also possible, whereby the server
   sends a challenge in 401 errors in headers.  If the server gives the
   client a choice of mechanisms (multiple WWW-Authenticate header
   values) and the client picks one where the server sent a challenge,
   then the client consumes that message and POSTs subsequent ones to
   the indicated URI.



































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2.  Conventions used in this document

   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].














































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3.  API-Imposed Constraints

   To the extent that existing Application Programming Interfaces (APIs)
   assume specific styles of HTTP authentication message flows, if we
   want those APIs to support RESTauth backwards-compatibly, then those
   APIs may impose constraints on RESTauth.

   For example, the Android Account Manager API assumes a single round
   trip for authentication.  But the Android Account Manager could
   perform all but the last round trip on behalf of the application,
   then let the application perform the last round trip.  In order for
   that to work we need the authentication message exchange to be
   orthogonal to TCP/TLS connections - that is, we need it to be
   possible to use multiple TCP/TLS connections for completing a single
   authentication exchange.

   A typical constraining characteristic might be that an API assumes
   the use of GET with tokens encoded into the URI, or that the API
   makes no room for the use of headers in authentication message
   exchanges.

   One way to work around such constraints may be to provide various
   options in this framework.  Another might be to use OAuth 1.0
   [RFC5849] or 2.0 [I-D.ietf-oauth-v2] as a bridge: the API would use
   this framework under the covers then obtain OAuth credentials from
   the server that the application can then use in any way that the
   API's form allows for.

   [[anchor1: TODO: Add a table/list of various APIs and their
   characteristics that might constrain this framework.]]





















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4.  Protocol

   The are very few normative protocol elements here besides the outline
   given in Section 1.  The normative protocol elements are:

   o  the form of the WWW-Authenticate header values for RESTauth
      mechanisms;

   o  several new headers for advertising negotiable parameters that are
      orthogonal to WWW-Authenticate;

   o  the POSTing of authentication messages from the client, with the
      initial client authentication message going to either a pre-agreed
      URI or to a URI named in the WWW-Authenticate headers;

   o  the creation of a session URI as a result of the initial POST, and
      the subsequent POSTing of any additional authentication messages
      to the session URI;

   o  the new session URI resource representation resulting from POSTs
      being the server's response authentication message, if any;

   o  the DELETEion of session URIs as signaling logout;

   o  a new header for referencing session URIs in normal HTTP requests;

   o  the use of channel binding [RFC5056] to TLS [RFC5246] for session
      protection;

   o  the use of session keys as an option for integrity protection when
      TLS is not used (a light-weight security mode).

4.1.  Negotiable Parameters

   As can be seen in the ABNF in the preceding section, the server can
   offer some negotiable parameters.  These are:

   o  Mechanism names;

   o  Channel binding types;

   o  Session binding types;

   o  Replay protection;

   Each WWW-Authenticate header value offers a single mechanism and
   negotiable parameters for it.  The WWW-ChannelBinding-Types header
   allows the server to offer channel binding types.



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4.1.1.  Strong Binding to TLS

   Strong binding to TLS is provided via channel binding [RFC5056].
   When a RESTauth mechanism provides strong authentication of the
   service to the user, the combination of RESTauth and channel binding
   results in strong authentication of the server to the user even
   though TLS is used for session transport protection.

4.1.2.  WWW-Authenticate Header Value Prefix Syntax

   The ABNF for RESTauth WWW-Authenticate header values is as follows:

         challenge           = ( "RA-" mechname SP restauth-challenge )
         mechname            = TBD
         restauth-challenge  = ( login-uri SP session-types SP
                                 replay-prot SP *1(mech-challenge) )
         login-uri           = absoluteURI
         session-types       = "s=" session-type /
                               (session-type ":" session-types)
         session-type        = "cookie" / "session-ID" / "MAC"
         replay-prot         = "r=" ("yes" / "no")
         ; TODO: add production for
         ;       mech-challenge as a base64 string
         ; TODO: add MAC algorithm offers for alg agility?

                      Figure 1: WWW-Authenticate ABNF

   For a DIGEST-like mechanism it might look like "WWW-Authenticate: RA-
   Digest-SHA-256 tls-server-end-point session-ID no HE4SgWGrd/
   3+O7t16HqusA==".  For example, the mechname for the Kerberos V5 GSS-
   API mechanism might be "gss-krb5", and a WWW-Authenticate header
   value for it might look like "WWW-Authenticate: RA-gss-krb5
   http://foo.example/restauth-login tls-server-end-point session-ID
   no".

   Note that mechanisms that may be used include: GSS mechanisms, SASL
   mechanisms, ad-hoc mechanisms, and so on.

4.1.3.  WWW-ChannelBinding-Types Header

   A new header is added by which servers MUST indicate which channel
   binding [RFC5056] types -if any- they support for RESTauth
   authentication; if the server does not support channel binding then
   this header MUST be absent.  The header is named WWW-ChannelBinding-
   Types.  Its values are channel binding types from the channel binding
   type registry [RFC5929].





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4.1.4.  WWW-ChannelBinding-Type Header

   A new header is added by which clients MUST indicate what channel
   binding type they used when POSTing RESTauth authentication messages,
   if any; if the client did not use channel binding then this header
   MUST be absent.  If the mechanism used has its own method for
   indicating the use of channel binding, then this header MAY be
   ommitted.  The header is named WWW-ChannelBinding-Type.  Its value is
   a channel binding type from the channel binding type registry
   [RFC5929].

4.1.5.  WWW-SessionBinding-Type Header

   A new header is added by which clients MUST indicate what session
   binding type they choose when POSTing RESTauth authentication
   messages.  The header is named WWW-SessionBinding-Type.  Its value is
   a session binding type as shown in Figure 1.  This header SHOULD be
   present in RESTauth authentication HTTP requests, but may be ommitted
   when the selected mechanism provides its own session binding facility
   that is distinct from RESTauth's (this helps adapt OAuth to RESTauth
   with minimal or no changes).

4.1.6.  WWW-ReplayProtection Header

   A new header is added by which clients MUST indicate whether they
   desire replay protection when POSTing RESTauth authentication
   messages.  The header is named WWW-SessionBinding-Type.  Its value is
   "yes" or "no" (defaults to "no" if absent) as shown in Figure 1.

   Replay protection is to be used only when TLS [RFC5246] is not, and
   only if a session binding type of "MAC" is also requested.

4.2.  Protocol Flow

   RESTauth can be initiated by a client that knows a priori that it
   needs to or wants to use RESTauth.  Servers can also tell clients
   that access to certain resources require authentication, possibly
   including RESTauth mechanisms.  When the server tells the client that
   it must authenticate, the server may also give the client an initial
   authentication message for one or more mechanisms.

   When the client knows a priori that it must authenticate then the
   client MUST know the RESTauth login URI a priori as well, as well as
   negotiable parameters, all of which the client might know from either
   an application protocol specification, or from caching this
   information from earlier RESTauth exchanges.

   The server MUST use a 401 HTTP status code and WWW-Authenticate



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   headers to inform the client of the need to authenticate in order to
   access a given resource.  For RESTauth mechanisms the WWW-
   Authenticate header values MUST conform to the ABNF given in
   Section 4.1.2.

   To proceed the client chooses a suitable authentication mechanism
   (for which, presumably, it has credentials for a desired client
   identity), possibly a channel binding type, possibly a session type,
   and whether to use replay protection.

4.2.1.  One Round Trip Optimization: Challenges Born in WWW-Authenticate
        Headers

   Some mechanisms may optimize the protocol flow by allowing the server
   to include challenges in the 401 response's WWW-Authenticate header
   values.  DIGEST-MD5 works this way, for example, sending a challenge
   nonce to be fed into the digest function (along with other client-
   side inputs).

   RESTauth allows this, but this feature is OPTIONAL: it must always be
   possible for a client to initiate RESTauth without first obtaining a
   challenge in a WWW-Authenticate header value, in which case the
   client must incur an extra protocol leg by obtaining the challenge
   (if it is at all necessary) in the server's reply to the client's
   first authentication message.  There are two reasons for making this
   optional:

   1.  to allow client applications that know a priori that they must
       authenticate, requiring no further negotiation;

   2.  to support authentication frameworks that require that the client
       initiate authentication message exchanges.

   A challenge may consist of a nonce, some encrypted or MACed nonce, a
   time-stamp, certificates and digital signatures, etcetera.  The
   server may include a login URI in challenge-laden WWW-Authenticate
   headers where the login URI encodes secure state regarding the
   challenge (e.g., the challenge encrypted in a symmetric key known
   only to the server).

4.3.  Session Binding Types: Cookie, URI, and MAC

   A notion of session binding type is added for binding HTTP requests
   to specific RESTauth login sessions.  Three types are provided:







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   Cookies  The traditional HTTP cookie approach to session binding;

   Session URI  HTTP requests carry a WWW-Session-URI header identifying
      the session(s) (similar to cookies, but without all the associated
      baggage);

   MAC  HTTP requests carry a WWW-Session-URI header identifying the
      session(s) and a WWW-Session-MAC header that carries a MAC or MACs
      binding the session URI(s) to the request.

4.3.1.  The New WWW-Session-URI Header

   A new HTTP header is added called WWW-Session-URI whose values
   consist of session URIs.  At least one session URI MUST be included.
   Each session URI is an absoluteURI.  Session URIs MUST NOT have
   unescaped commas (',') embedded in them.  Servers MAY fail to
   implement support for multiple session URIs being referenced by a
   single request, in which case they MUST answer with error code <TBD>.
   Servers MUST validate the session URI before processing the request;
   if the session URI is invalid the server MUST respond with a 401 (or
   TBD?) status code.

   Note that referencing multiple session URIs is permitted, but this
   may not be meaningful for the application, thus the server MAY reject
   this (TODO: specify a status code for this?).

   [[anchor2: I can imagine a webmail application where a client can be
   logged in as multiple users and get a unified view of the users'
   mailboxes.  This seems unlikely, but why rule out such use cases?]]

4.3.2.  The New WWW-Session-MAC Header

   [[anchor3: Describe the header, its values, algorithm agility, and
   what the MAC is to be taken over.  Note too that this cannot apply to
   request contents as we have to consider chunking, and besides, a MAC
   of contents really has to go as a trailer, not a header.]]

4.3.3.  A MAC Trailer??

   [[anchor4: ...  This is only needed for RESTauth *without* TLS, which
   will probably not be the common mode of use for RESTauth... unless we
   can produce a MAC trailer extension for HTTP/2.0, in which case this
   may well become a common mode of RESTauth usage.]]








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5.  HTTP "Routing" and Authentication

   It is common to deploy HTTP services with load-balanced servers
   behind a load balancer and TLS concentrator.  Other techniques may
   also result in a multiplicity of servers acting on behalf of a single
   service.  The load balancers may even behave like routers and route
   HTTP requests to the same server for all requests in a single
   connection, or even route HTTP requests according to the verb and
   resource.  It helps to be able to have a notion of authenticated
   sessions that can be referenced by all servers responding to a given
   service name.

   The server end of a RESTauth authentication message exchange may be
   terminated by one server, by many servers sharing session state (via
   the resources named by session URIs), or by a server-side HTTP
   router.  Once a RESTauth session is established we assume that all
   servers responding to the same service name will be able to access
   the session resource, validate session URIs, and obtain keys for
   computing and validating session binding MACs.  Alternatively, the
   router may take responsibility for session binding and signal
   authorization information from the established session to the HTTP
   servers behind the router (however, we do not here specify any
   methods for such signaling).

   By using REST for the authentication message exchange we allow this
   disconnection between "session" and "connection", which therefore
   facilitates "routing" of HTTP requests and even off-loading of
   authentication and/or session binding to HTTP "routers".

   This approach should be flexible enough for all existing
   architectures for deploying HTTP services.




















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6.  In-band HTTP Authentication Alternatives

   RESTauth is "out-of-band" in the sense that the authentication
   messages are exchanged independently of the application's requests
   for normal resources.  Of course, RESTauth exchanges may well (and
   often will) happen in the same TCP/TLS connection as normal
   application requests, so RESTauth is not really out-of-band.  We use
   "out-of-band" and "in-band" very loosely in this section.

   There exist several "in-band" HTTP authentication alternatives where
   the authentication message exchanges happen in the context of
   application resources.  Here the HTTP verb and resource are
   application-specific and have nothing to do with authentication, and
   the authentication messages are exchanged via HTTP request and
   response headers with the server responding with a 401 status code
   until authentication is complete.

   The extant "Basic" and "DIGEST-MD5" [RFC2617] HTTP authentication
   methods, as well as HTTP/Negotiate [RFC4559] are "in-band" HTTP
   authentication methods.

   In so far as an in-band authentication method results in a cookie or
   session URI/ID the distinction between in-band and out-of-band is
   almost trivial, as described above: authentication messages in
   headers vs. bodies, and HTTP verb and URL.  However, if in-line
   authentication methods are strongly tied to the TCP/TLS connections
   over which they were utilized then that is a big disadvantage over
   RESTauth: each connection requires re-authenticating, and support for
   HTTP routing schemes is not clear.

   HTTP/Negotiate is more troublesome because historically it has
   required re-authentication per-HTTP request(!).

   Even if the only difference between in-band and out-of-band is a
   trivial one, using the REST pattern means that authentication can be
   implemented using with no help from the HTTP stack (even though it's
   desirable to have it implemented within/by the HTTP stack), whereas
   there may not be a way to implement in-band authentication without
   help from the HTTP stack for some stacks.












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7.  Sample/Potential RESTauth Authentication Mechanisms

   Here we describe (informatively, for the time being) how to use or
   adapt a variety of authentication mechanisms, from SSHv2, IKEv2,
   SASL, GSS-API, and other frameworks, so as to quickly gain a set of
   usable mechanisms, both, specification- and implementation-wise.
   This section is also intended to show that adding RESTauth mechanisms
   is easy.

7.1.  OAuth via RESTauth

   OAuth 1.0 RFC5849 and OAuth 2.0 [I-D.ietf-oauth-v2] are commonly
   deployed.  Being able to use OAuth via RESTauth would be useful.  We
   attempt to make RESTauth such that at least for OAuth 1.0 there is a
   standard way to use OAuth such that it conforms to RESTauth.

7.1.1.  OAuth 1.0

   For OAuth 1.0 [RFC5849] the "form-encoded body" form (see section
   3.5.2 of [RFC5849]) of OAuth 1.0 conforms to RESTauth without further
   changes.

7.1.2.  OAuth 2.0

   [It looks like OAuth 2.0 [I-D.ietf-oauth-v2] also uses POST to send
   tokens to the server, and it looks like it too effectively conforms
   to RESTauth.]

7.2.  Adapting SSHv2 Authentication Mechanisms to RESTauth

   SSHv2 "userauth" mechanisms [RFC4252] typically involve a digital
   signature (or similar) of an SSHv2 session ID.  There is no such
   thing as an SSHv2 session ID in HTTP.  A session URI cannot serve as
   a stand-in for an SSHv2 session ID because a) the session URI is an
   outcome of authentication in RESTauth, b) to prevent cut-n-paste and
   replay attacks the client and the server both must contribute to the
   entropy of the session ID that is signed by the client.

   In order to adapt SSHv2 userauth methods properly (i.e., securely),
   we have replace the SSHv2 session ID in the to-be-signed data with a
   hash of the channel binding and nonces contributed by the client and
   the server.  As an optimization the server nonce can be sent as a
   challenge (this saves a round trip).

7.2.1.  RESTauth Mechanism Names for SSHv2 Userauth Methods

   For hash agility reasons the hash function name is part of the SSHv2
   RESTauth mechanism name.  To avoid "multi-level negotiation" the



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   SSHv2 userauth method name is also part of the RESTauth mechanism
   name.

   The RESTauth mechanism name form for SSHv2 userauth methods, then,
   is: ssh-<SSHv2-userauth-method-name>-<hash-function-name>.

   The following RESTauth mechanisms are defined here:

   o  ssh-publickey-SHA-256

   o  ssh-hostbased-SHA-256

7.2.2.  Nonces

   The client and the server must each contribute 128-bit nonces.

7.2.3.  "Session ID"

   The ssh-publickey-SHA-256 and ssh-hostbased-SHA-256 mechanisms use
   the following instead of a traditional SSHv2 session ID:

   o  SHA-256(channel_binding || server_nonce || client_nonce)

   Here the <channel_binding> is as per-[RFC5056]: the channel binding
   type name, followed by the channel binding data (e.g., 'tls-server-
   end-point' followed by the server EE certificate as sent in the
   server's TLS Certificate message).

   Note that use of channel binding when using SSHv2 mechanisms is
   REQUIRED so as to defeat cut-n-paste attacks by weakly-authenticated
   servers.

7.3.  Adapting IKEv2 Authentication Mechanisms to RESTauth

   [[anchor5: TBD.]]

7.3.1.  Adapting IKEv2 Password Authenticated Connection Establishment
        (PACE) to RESTauth

   [[anchor6: TBD.]]

7.4.  Using SASL Authentication Mechanisms with RESTauth

   Simple Authentication and Security Layers (SASL) [RFC4422] is a
   simple, pluggable framework for authentication mechanisms.

   To use a SASL mechanism in RESTauth just prefix "SA-" to the SASL
   mechanism name and use that as the RESTauth mechanism name.  If the



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   SASL mechanism is server-initiated then the server's challenge is
   sent in the server's WWW-Authenticate header value as described
   above.  All other SASL authentication messages are exchanged as
   described above (i.e., via POSTs, first to the login URI, then to the
   session URI, with response messages as the new representation of the
   session resource).

   The HTTP status code functions as the application's outcome of
   authentication message.  If SASL succeeds but authorization fails
   then the server should respond with a 401 status code to the POST of
   the final SASL authentication message from the client.

   The server's WWW-Authenticate header values function as the mechanism
   listing operation.  SASL security considerations [RFC4422] [RFC5801]
   apply (particularly regarding the negotiation of channel binding
   support).

7.4.1.  Using SCRAM in RESTauth

   The Salted Challenge Response Authentication Mechanism (SCRAM)
   [RFC5802] is a DIGEST-like mechanism for SASL.  Nothing special is
   needed to use SCRAM versus any other SASL mechanism, except for a
   round trip optimized form of SCRAM, if we decide to pursue that (see
   Section 7.4.2).

   The following figure shows what SCRAM in RESTauth looks like.  Note
   that the resource representations are taken verbatim from [RFC5802].
























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     C->S: GET /some-resources HTTP/1.1
           Host: A.example

     S->C: HTTP/1.1 401 Unauthorized
           WWW-Authenticate: RA-SA-SCRAM-SHA-1 \
                             http://A.example/rest-sa-scram \
                             s=session-ID,MIC r=no
           WWW-ChannelBinding-Types: tls-server-end-point

     C->S: POST /rest-sa-scram HTTP/1.1
           Host: A.example
           WWW-ChannelBinding-Type: tls-server-end-point
           WWW-SessionBinding-Type: session-ID
           Content-Type: application/octet-stream
           Content-Length: nnn

           n,,n=user,r=fyko+d2lbbFgONRv9qkxdawL

     S->C: HTTP/1.1 201
           Location http://A.example/restauth-9d0af5f680d4ff46
           Content-Type: application/octet-stream
           Content-Length: nnn

           r=fyko+d2lbbFgONRv9qkxdawL3rfcNHYJY1ZVvWVs7j,
           s=QSXCR+Q6sek8bf92,i=4096

     C->S: POST /restauth-9d0af5f680d4ff46 HTTP/1.1
           Host: A.example
           Content-Type: application/octet-stream
           Content-Length: nnn

           c=biws,r=fyko+d2lbbFgONRv9qkxdawL3rfcNHYJY1ZVvWVs7j,
           p=v0X8v3Bz2T0CJGbJQyF0X+HI4Ts=

     S->C: HTTP/1.1 200
           Content-Type: application/octet-stream
           Content-Length: nnn

           v=rmF9pqV8S7suAoZWja4dJRkFsKQ=

                        Figure 2: RESTauth w/ SCRAM

7.4.2.  Using SCRAM with Round Trip Optimization in RESTauth

   [[anchor7: This might work by having the authentication ID function
   as the salt and the server offering a challenge nonce and iteration
   count in its optimistic challenge.  However, it's not clear that a
   round trip optimized form of SCRAM is desirable.]]



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   The following figure shows what a round trip optimized RESTauth w/
   SCRAM exchange might look like.

   [[anchor8: NOTE: SCRAM was not intended to be used this way.  In
   particular this approach forces the use of an algorithmic salt, to be
   derived only from either the username or the username and the
   server's name (or else to be remembered by the user, but that's not
   likely).]]

     C->S: GET /some-resources HTTP/1.1
           Host: A.example

     S->C: HTTP/1.1 401 Unauthorized
           WWW-Authenticate: RA-SA-SCRAM-SHA-1 \
                             http://A.example/rest-sa-scram \
                             s=session-ID,MIC r=no \
                             r=fyko+d2l...JY1ZVvWVs7j,i=4096
           WWW-ChannelBinding-Types: tls-server-end-point

     C->S: POST /rest-sa-scram HTTP/1.1
           Host: A.example
           WWW-ChannelBinding-Type: tls-server-end-point
           WWW-SessionBinding-Type: session-ID
           Content-Type: application/octet-stream
           Content-Length: nnn

           n,,n=user,r=fyko+d2lbbFgONRv9qkxdawL,
           c=biws,r=fyko+d2lbbFgONRv9qkxdawL3rfcNHYJY1ZVvWVs7j,
           p=v0X8v3Bz2T0CJGbJQyF0X+HI4Ts=

     S->C: HTTP/1.1 200
           Content-Type: application/octet-stream
           Content-Length: nnn

           v=rmF9pqV8S7suAoZWja4dJRkFsKQ=

             Figure 3: RESTauth w/ round trip optimized SCRAM

7.5.  Using GSS-API Authentication Mechanisms with RESTauth

   The Generic Security Services Application Programming Interface (GSS-
   API) [RFC2743] is another pluggable mechanism framework.  Any GSS-API
   mechanism that supports channel binding [RFC5056] can be used as SASL
   mechanisms via the "SASL/GS2" bridge [RFC5801].  This includes the
   Kerberos V5 GSS-API mechanism [RFC4121].






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8.  IANA Considerations

   TBD (header registrations, ...)
















































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9.  Security Considerations

   This entire document deals with security considerations.  [Add more,
   like about channel binding, same-origin-like constraints on the login
   and session absolute URIs', ...]














































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10.  TODO

   [[anchor9: Add references (to HTTP/2.0, CGI/fCGI, ...).]]

   [[anchor10: Describe MAC session binding option and replay protection
   in detail.  Describe how to extract keys for MAC keying from SASL/
   GSS/PACE.]]

   [[anchor11: Figure out how to adapt IKEv2 password-based methods to
   RESTauth.  This may not be worthwhile (since each method tends to
   depend heavily on the entire IKEv2 framework in ways that add
   messaging that we'd not need in RESTauth).]]







































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11.  References

11.1.  Normative References

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

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

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

   [RFC5056]  Williams, N., "On the Use of Channel Bindings to Secure
              Channels", RFC 5056, November 2007.

   [RFC5929]  Altman, J., Williams, N., and L. Zhu, "Channel Bindings
              for TLS", RFC 5929, July 2010.

11.2.  Informative References

   [RFC5849]  Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849,
              April 2010.

   [I-D.ietf-oauth-v2]
              Hardt, D., "The OAuth 2.0 Authorization Framework",
              draft-ietf-oauth-v2-31 (work in progress), August 2012.

   [RFC4422]  Melnikov, A. and K. Zeilenga, "Simple Authentication and
              Security Layer (SASL)", RFC 4422, June 2006.

   [RFC5802]  Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams,
              "Salted Challenge Response Authentication Mechanism
              (SCRAM) SASL and GSS-API Mechanisms", RFC 5802, July 2010.

   [RFC4252]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, January 2006.

   [RFC4559]  Jaganathan, K., Zhu, L., and J. Brezak, "SPNEGO-based
              Kerberos and NTLM HTTP Authentication in Microsoft
              Windows", RFC 4559, June 2006.




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   [RFC6631]  Kuegler, D. and Y. Sheffer, "Password Authenticated
              Connection Establishment with the Internet Key Exchange
              Protocol version 2 (IKEv2)", RFC 6631, June 2012.

   [RFC2743]  Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743, January 2000.

   [RFC5801]  Josefsson, S. and N. Williams, "Using Generic Security
              Service Application Program Interface (GSS-API) Mechanisms
              in Simple Authentication and Security Layer (SASL): The
              GS2 Mechanism Family", RFC 5801, July 2010.

   [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,
              July 2005.



































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Author's Address

   Nicolas Williams
   Cryptonector, LLC

   Email: nico@cryptonector.com













































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