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Network Working Group                                        N. Williams
Internet-Draft                                              Cryptonector
Intended status: Informational                           August 11, 2012
Expires: February 12, 2013


  RESTful Authentication Pattern for the HyperText Transport Protocol
                                 (HTTP)
                    draft-williams-http-rest-auth-00

Abstract

   This document proposes a "RESTful" pattern of authentication for
   HTTP/1.0, 1.1, and 2.0.  The existing 401 status code and WWW-
   Authenticate header are used to indicate that authentication is
   required and for negotiation purposes.  The client POSTs an initial
   authentication message to an indicated login URI, and reply messages
   are returned as new representations of a session resource named by a
   session URI.

   This approach has a number of benefits: it can be implemented with or
   without help from the HTTP stack, it can be universally implemented
   on the server side using the Common Information Gateway (CGI) and
   FastCGI, it results in a session Uniform Resource Identifier (URI)
   that can be DELETEd to logout, it is completely orthogonal to any
   HTTP "routers" and proxies, and it naturally (i.e., without changing
   HTTP) handles multi-legged authentication mechanisms.

   Among other features supported are: channel binding, an optional
   round trip optimization for challenge/response mechanisms,
   somecryptographic protection options for clients that don't use
   Transport Layer Security (TLS), stronger authentication of servers/
   services to users (where authentication mechanisms provide that) and
   more.

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



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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 12, 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
   (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.      Protocol . . . . . . . . . . . . . . . . . . . . . . . . .  7
   3.1.    Negotiable Parameters  . . . . . . . . . . . . . . . . . .  7
   3.1.1.  WWW-Authenticate Header Value Prefix Syntax  . . . . . . .  8
   3.1.2.  WWW-ChannelBinding-Types Header  . . . . . . . . . . . . .  8
   3.1.3.  WWW-ChannelBinding-Type Header . . . . . . . . . . . . . .  8
   3.1.4.  WWW-SessionType Header . . . . . . . . . . . . . . . . . .  9
   3.1.5.  WWW-ReplayProtection Header  . . . . . . . . . . . . . . .  9
   3.2.    Protocol Flow  . . . . . . . . . . . . . . . . . . . . . .  9
   3.2.1.  One Round Trip Optimization: Challenges Born in
           WWW-Authenticate Headers . . . . . . . . . . . . . . . . .  9
   3.3.    Session Binding Types: Cookie, URI, and MAC  . . . . . . . 10
   3.3.1.  The New WWW-Session-URI Header . . . . . . . . . . . . . . 10
   3.3.2.  The New WWW-Session-MAC Header . . . . . . . . . . . . . . 10
   3.3.3.  A MAC Trailer??  . . . . . . . . . . . . . . . . . . . . . 11
   4.      HTTP "Routing" and RESTauth  . . . . . . . . . . . . . . . 12
   5.      Sample/Potential RESTauth Authentication Mechanisms  . . . 13
   5.1.    Adapting SSHv2 Authentication Mechanisms to RESTauth . . . 13
   5.1.1.  Adaptinve SSHv2 'publickey userauth' to RESTauth . . . . . 13
   5.1.2.  Adaptinve SSHv2 'hostbased userauth' to RESTauth . . . . . 13
   5.2.    Adapting IKEv2 Authentication Mechanisms to RESTauth . . . 13
   5.2.1.  Adaptinve IKEv2 Password Authenticated Connection
           Establishment (PACE) to RESTauth . . . . . . . . . . . . . 13
   5.3.    Using SASL Authentication Mechanisms with RESTauth . . . . 13
   5.3.1.  Using SCRAM in RESTauth  . . . . . . . . . . . . . . . . . 13
   5.3.2.  Using SCRAM with Round Trip Optimization in RESTauth . . . 13
   5.4.    Using GSS-API Authentication Mechanisms with RESTauth  . . 13
   6.      IANA Considerations  . . . . . . . . . . . . . . . . . . . 14
   7.      Security Considerations  . . . . . . . . . . . . . . . . . 15
   8.      TODO . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
   9.      References . . . . . . . . . . . . . . . . . . . . . . . . 17
           Author's Address . . . . . . . . . . . . . . . . . . . . . 18
















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1.  Introduction

   We propose a pattern for HTTP authentication mechanisms that, by
   being "RESTful", obtains a number of benefits:

   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
      web 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: initial
   authentication messages are POSTed to an agreed-upon or indicated
   resource, which then results in a new resource being created with the
   authentication reply message as the new resource's representation.
   Thereafter any additional authentication message exchanges needed
   (for multi-legged mechanisms) are POSTed to the new resource without
   a new resource being created.  The resource created by the POSTing of
   the initial authentication mechanism identifies the resulting
   session, and its URI is known as the session URI.  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 (not much else can be sent of value in an initial



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   authentication message from the server besides a challenge,
   negotiation parameters, and, perhaps, a digital signature) in 401
   errors in headers.  If the server gives the client has a choice of
   mechanisms and the client picks one where the server sent the initial
   authentication message, then the client consumes that message and
   POSTs subsequent ones to the agreed URI.

   This document replaces [I-D.williams-rest-gss].











































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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.  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 paramters 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 signalling logout;

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

   o  the use of channel binding to TLS for session protection;

   o  the use of session keys as an option for integrity protection when
      TLS is not used.

3.1.  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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3.1.1.  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

                                 Figure 1

   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.

3.1.2.  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].

3.1.3.  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.  The header is named WWW-ChannelBinding-Type.  Its
   value is a channel binding type from the channel binding type
   registry [RFC5929].



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3.1.4.  WWW-SessionType 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 MUST be
   present in RESTauth authentication HTTP requests.

3.1.5.  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.

3.2.  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
   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 3.1.1.

   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.

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

   Some mechanisms may optimize the protocol flow by allowing the server



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   to include challenges in the 401 response's WWW-Authenticate header
   values.  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.  The reason that this
   optimization is optional is to allow the implementation of RESTauth
   mechanisms with frameworks that only support client-initiated
   authentication.

   A challenge may consist of a nonce, some encrypted or MACed nonce, a
   timestamp, and even seemingly unrelated contents such as certificates
   and digital signatures.  The server MAY include a login URI in
   challenge-laden WWW-Authenticate headers where the login URI encodes
   secure state regarding the challenge.

3.3.  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:

   Cookies  The traditional web 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.

3.3.1.  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.

3.3.2.  The New WWW-Session-MAC Header

   [[anchor1: Describe the header, its values, algorithm agility, and
   what the MAC is to be taken over.  Note too that this cannot apply to



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   request contents as we have to consider chunking, and besides, a MAC
   of contents really has to go as a trailer, not a header.]]

3.3.3.  A MAC Trailer??

   [[anchor2: ...]]













































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4.  HTTP "Routing" and RESTauth

   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 signalling).

   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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5.  Sample/Potential RESTauth Authentication Mechanisms

   [[anchor3: TODO: Describe how to use or adapt a variety of
   authentication mechanisms, from SSHv2, IKEv2, SASL, GSS-API, and
   other frameworks, to gain a set of usable mechanisms quickly, both,
   specification- and implementation-wise.  Although I've not done this
   yet, it seems likely to be quite simple to adapt all these
   authentication mechanism types to RESTauth.]]

5.1.  Adapting SSHv2 Authentication Mechanisms to RESTauth

5.1.1.  Adaptinve SSHv2 'publickey userauth' to RESTauth

5.1.2.  Adaptinve SSHv2 'hostbased userauth' to RESTauth

5.2.  Adapting IKEv2 Authentication Mechanisms to RESTauth

5.2.1.  Adaptinve IKEv2 Password Authenticated Connection Establishment
        (PACE) to RESTauth

5.3.  Using SASL Authentication Mechanisms with RESTauth

5.3.1.  Using SCRAM in RESTauth

5.3.2.  Using SCRAM with Round Trip Optimization in RESTauth

5.4.  Using GSS-API Authentication Mechanisms with RESTauth
























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6.  IANA Considerations

   TBD (header registrations, ...)
















































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7.  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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8.  TODO

   [[anchor4: Add references (to HTTP, CGI/fCGI, SSHv2, IKEv2, SASL,
   GSS, PACE, ...).]]

   [[anchor5: Describe MAC session binding option and replay protection
   in detail.]]

   [[anchor6: Add text to and complete sections describing how to use
   various existing security mechanisms with RESTauth, such as SASL,
   GSS-API, and other mechanisms.]]

   [[anchor7: Add text to and complete sections describing mechanisms
   for adapting to RESTauth SSHv2 publickey, SSHv2 host-based
   authentication, IKEv2 methods, and other such authentication
   mechanisms as a way of showcasing RESTauth.]]



































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9.  References

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

   [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.

   [I-D.williams-rest-gss]
              Williams, N., "RESTful Hypertext Transfer Protocol
              Application-Layer Authentication Using Generic Security
              Services", draft-williams-rest-gss-02 (work in progress),
              July 2012.
































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Author's Address

   Nicolas Williams
   Cryptonector, LLC

   Email: nico@cryptonector.com













































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