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Versions: 00

Internet Engineering Task Force                             E. Prodromou
Internet-Draft                                           StatusNet, Inc.
Intended status: Experimental                          September 6, 2012
Expires: March 10, 2013


          HTTP Authentication: Dialback Access Authentication
                      draft-prodromou-dialback-00

Abstract

   This specification defines the Dialback Access Authentication Scheme.
   It provides a way for HTTP clients to identify an Internet host or
   account responsible for an HTTP request, and for HTTP servers to
   verify that identity by sending a token to a declared dialback
   endpoint.

   The specification defines a new HTTP authentication scheme,
   "Dialback".  It also defines a new link relation, "dialback", to
   specify the endpoint for the dialback verification.  Finally, it
   defines the interface for the dialback endpoint.

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

   This Internet-Draft will expire on March 10, 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



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   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.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . . . 3
   2.  Authentication scheme . . . . . . . . . . . . . . . . . . . . . 3
   3.  Dialback endpoint discovery . . . . . . . . . . . . . . . . . . 4
   4.  Dialback verification endpoint  . . . . . . . . . . . . . . . . 4
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     5.1.  Host authentication . . . . . . . . . . . . . . . . . . . . 5
     5.2.  Webfinger authentication  . . . . . . . . . . . . . . . . . 6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
     6.1.  Authentication scheme . . . . . . . . . . . . . . . . . . . 7
     6.2.  Link relation . . . . . . . . . . . . . . . . . . . . . . . 7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
     7.1.  Replay attacks  . . . . . . . . . . . . . . . . . . . . . . 7
     7.2.  Link discovery  . . . . . . . . . . . . . . . . . . . . . . 7
     7.3.  Endpoint  . . . . . . . . . . . . . . . . . . . . . . . . . 8
     7.4.  Confidentiality . . . . . . . . . . . . . . . . . . . . . . 8
     7.5.  Data integrity  . . . . . . . . . . . . . . . . . . . . . . 8
     7.6.  Denial of service . . . . . . . . . . . . . . . . . . . . . 8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 9
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 9




















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1.  Introduction

   HTTP/1.1 [RFC2616] has an extensible authentication mechanism using
   the "Authorization" header.  Basic and Digest Authentication
   [RFC2617] are two authentication schemes for HTTP/1.1.  OAuth 1.0
   [RFC5849] is another.

   All of these authentication schemes assume that the HTTP server is
   able to validate the authentication credentials.  With distributed
   publishing and social networking applications, however, the security
   domain may be separate from the resource domain.  In addition, the
   resource and security domains may have no previously-negotiated
   relationship.

   With dialback authentication, an HTTP client can authenticate as a
   host or Webfinger address without creating a previous relationship.
   The HTTP server verifies the identity using a dialback endpoint
   specified by the host or Webfinger address.

   Because dialback authentication requires one or more additional
   requests from server to client, its intended use is for bootstrapping
   longer-term relationships, such as dynamic registration of OAuth
   clients.  It can also be useful for single use requests.

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.  Authentication scheme

   This spec adds a new Authorization type, "Dialback".

   The header has the following optional elements:

   host    The host authorizing the request.

   webfinger  The webfinger account authorizing the request.

   token   An opaque value used to confirm the request authorization

   Exactly one of "host" or "webfinger" is required.

   "token" is always required.





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3.  Dialback endpoint discovery

   To validate the token, the server must identify a dialback endpoint
   for the host or Webfinger address.

   For a host parameter, the server SHOULD use Web Host Metadata
   [RFC6415] to find the endpoint.  It will have the link relation
   "dialback".

   For a webfinger parameter, the server SHOULD use Webfinger
   [I-D.jones-appsawg-webfinger] to find the endpoint with the link
   relation "dialback".


4.  Dialback verification endpoint

   To confirm, the server makes an HTTP POST request to the dialback
   endpoint.  The request MUST have the Content-Type application/
   x-www-url-encoded.

   The HTTP request has the following parameters.

   host    The host value provided in the original Authorization header.

   webfinger  The webfinger value provided in the original Authorization
           header.

   token   The token provided in the original Authorization header.

   url     The URL that the original request was made to.

   date    The Date header on the original request.

   The request MUST include exactly one of "host" or "webfinger".

   The request MUST include the "token", "url" and "date" parameters.

   All parameters MUST be encoded in the body of the request.

   If the token is valid, the endpoint SHOULD return a 200 OK or 204 No
   Content result.

   If the token is invalid, the endpoint SHOULD return a 400 Bad Request
   result.







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5.  Examples

5.1.  Host authentication

   o  The client sends an HTTP request with an Authorization header:

   POST /some/endpoint HTTP/1.1
   Host: photo.example
   Date: Tue, 28 Aug 2012 09:41:21 -0400
   Content-Type: application/x-www-url-form-encoded
   Authorization: Dialback
                  host="checkin.example",
                  token="4430086d"

   arg1=186&arg2=50

                                   Figure 1

   o  The server checks that the Date: header is within an acceptable
      window (+/- 5 minutes recommended).

   o  The server checks that it hasn't seen this (host, url, token,
      date) tuple before.

   o  The server discovers a dialback confirmation endpoint at
      checkin.example.  Its rel type is "dialback".

   o  The server posts an HTTP request to confirm the token:

   POST /dialback HTTP/1.1
   Host: checkin.example
   Date: Tue, 28 Aug 2012 09:41:43 -0400
   Content-Type: application/x-www-url-form-encoded

   host=checkin.example&\
   token=4430086d&\
   url=http://photo.example/some/endpoint&\
   date=Tue%2C%2028%20Aug%202012%2009%3A41%3A21%20-0400

                                   Figure 2

      Note: the "\" character is used here to indicate the line wrapping
      in the request content and is not part of the content itself.

   o  checkin.example returns 200 OK for a confirmation, 4xx for
      confirmation failure, 5xx for server failure.





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5.2.  Webfinger authentication

   o  The client sends an HTTP request with an Authorization header:

   GET /some/resource HTTP/1.1
   Host: photo.example
   Date: Tue, 28 Aug 2012 09:41:21 -0400
   Authorization: Dialback
                  webfinger="alice@checkin.example",
                  token="b3265cd5"

                                   Figure 3

   o  The server checks that the Date: header is within an acceptable
      window (+/- 5 minutes recommended).

   o  The server checks that it hasn't seen this (webfinger, url, token,
      date) tuple before.

   o  The server discovers a dialback confirmation endpoint for
      alice@checkin.example.  Its rel type is "dialback".

   o  The server posts an HTTP request to confirm the token:

   POST /dialback HTTP/1.1
   Host: checkin.example
   Date: Tue, 28 Aug 2012 09:41:43 -0400
   Content-Type: application/x-www-url-form-encoded

   webfinger=alice@checkin.example&\
   token=b3265cd5&\
   url=http://photo.example/some/resource&\
   date=Tue%2C%2028%20Aug%202012%2009%3A41%3A21%20-0400

                                   Figure 4

      Note: the "\" character is used here to indicate the line wrapping
      in the request content and is not part of the content itself.

   o  checkin.example returns 200 OK for a confirmation, 4xx for
      confirmation failure, 5xx for server failure.


6.  IANA Considerations







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6.1.  Authentication scheme

   This specification defines a new HTTP authentication scheme,
   "Dialback", per HTTP/1.1, part 7: Authentication
   [I-D.ietf-httpbis-p7-auth] to be registered at
   http://www.iana.org/assignments/http-authschemes.

   o  Authentication Scheme Name: Dialback

   o  Reference: (this document)

6.2.  Link relation

   This specification defines a new link relation type to be registered
   at http://www.iana.org/assignments/link-relations according to RFC
   5988 [RFC5988].

   o  Relation Name: dialback

   o  Description: a dialback token verification endpoint

   o  Reference: (this document)


7.  Security Considerations

7.1.  Replay attacks

   An attacker could capture the Authorization header of a request and
   replay the header for another payload.

   To prevent replay attacks, the server MUST NOT accept a request if it
   has already seen a request with the same host or webfinger, url,
   token, and date.

   Servers MAY mitigate storage requirements by rejecting requests with
   a Date: outside a fixed window. +/- 5 minutes from server time is
   reasonable.

7.2.  Link discovery

   An attacker could use DNS poisoning techniques to provide links to a
   false dialback endpoint.

   Clients supporting dialback SHOULD support TLS for host-meta and
   Webfinger discovery.

   HTTP servers SHOULD use the TLS endpoint for host-meta and Webfinger.



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   HTTP servers MAY fall back to the unencrypted equivalent.

7.3.  Endpoint

   An attacker could use DNS poisoning techniques to provide false
   responses to requests to the dialback verification endpoint.

   HTTP clients support dialback SHOULD use TLS for dialback endpoints.

   HTTP servers SHOULD require valid certificates for dialback
   endpoints.

7.4.  Confidentiality

   The dialback endpoint confirms that the host or Webfinger account is
   responsible for the HTTP request.

   An attacker could use brute-force methods to determine if the host or
   Webfinger account has made an HTTP request to a given URL.

   The dialback endpoint SHOULD NOT verify requests for dates outside a
   small window around the current time (+/- five minutes).

   The dialback endpoint SHOULD use large enough tokens to make brute-
   force attacks impractical.

7.5.  Data integrity

   Dialback authentication does not confirm the contents of the HTTP
   request.  For example, man-in-the-middle attack could replace the
   contents of a POST request with another payload, which would be
   verified.

   Servers SHOULD use TLS to prevent man-in-the-middle attacks.

7.6.  Denial of service

   Dialback authentication lets the HTTP client induce the HTTP server
   to make additional verification requests.

   By making requests with a host or webfinger parameter referring to a
   third party, a malicious client can cause extra HTTP requests to that
   third party.

   To avoid denial-of-service attacks, HTTP servers SHOULD cache the
   results of host-meta and Webfinger requests.





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8.  References

8.1.  Normative References

   [I-D.ietf-httpbis-p7-auth]
              Fielding, R., Lafon, Y., and J. Reschke, "HTTP/1.1, part
              7: Authentication", draft-ietf-httpbis-p7-auth-20 (work in
              progress), July 2012.

   [I-D.jones-appsawg-webfinger]
              Jones, P., Salgueiro, G., and J. Smarr, "WebFinger",
              draft-jones-appsawg-webfinger-06 (work in progress),
              June 2012.

   [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.

   [RFC5988]  Nottingham, M., "Web Linking", RFC 5988, October 2010.

   [RFC6415]  Hammer-Lahav, E. and B. Cook, "Web Host Metadata",
              RFC 6415, October 2011.

8.2.  Informative References

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


Author's Address

   Evan Prodromou
   StatusNet, Inc.

   Email: evan@status.net
   URI:   http://evan.status.net/







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