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HTTPBIS                                                       M. Thomson
Internet-Draft                                                   Mozilla
Intended status: Standards Track                             May 8, 2014
Expires: November 9, 2014


             Client Authentication over New TLS Connection
                     draft-thomson-httpbis-cant-00

Abstract

   This document defines an HTTP authentication scheme that can be added
   to an error response to indicate to a client that a successful
   response will only be provided over a new TLS connection, and only if
   the client has provided a certificate on that connection.

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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   This Internet-Draft will expire on November 9, 2014.

Copyright Notice

   Copyright (c) 2014 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
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   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions and Terminology . . . . . . . . . . . . . . .   2
   2.  Client Certificate Challenge  . . . . . . . . . . . . . . . .   2
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informational References  . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   Client authentication in HTTP sometimes relies on certificate-based
   authentication of clients in Transport Layer Security (TLS)
   [RFC5246].  Some uses of client authentication rely on TLS
   renegotiation, triggering renegotiation in response to a request for
   a particular resource.

   HTTP/2 [I-D.ietf-httpbis-http2] forbids the use of renegotiation,
   except for at the very beginning of a connection.  This makes
   addressing some client authentication use cases difficult.

   This document defines a new authentication scheme,
   "ClientCertificate", for use in HTTP authentication challenges
   [I-D.ietf-httpbis-p7-auth].  In combination with the 401
   (Unauthorized) status code, this indicates that the resource requires
   client authentication at the TLS layer in order to access it.

1.1.  Conventions and Terminology

   At times, this document falls back on shorthands for establishing
   interoperability requirements on implementations: the capitalized
   words "MUST", "SHOULD" and "MAY".  These terms are defined in
   [RFC2119].

2.  Client Certificate Challenge

   A new authentication scheme ([I-D.ietf-httpbis-p7-auth]) for the
   "WWW-Authenticate" and "Proxy-Authenticate" header fields is defined
   with the name "ClientCertificate".

   A challenge with this authentication scheme does not define any
   parameters except "realm".  The "realm" can be used to select an
   appropriate certificate, or if a certificate is already in use, to
   indicate the need for a different certificate.  Other challenge



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   parameters MAY be used to provide a client with information it can
   use to select an appropriate certificate.  Unknown parameters MUST be
   ignored.

   This challenge cannot be satisfied by constructing an Authorization
   header field [I-D.ietf-httpbis-p7-auth], it can only be satisfied by
   making the request on a TLS connection where an appropriate
   certificate has been provided by the client.

   To effectively use this authentication scheme, a new connection is
   needed for every protection space used by a given origin server.  A
   client can use the "ClientCertificate" challenge as a trigger to open
   a new connection and to use client authentication on that connection.
   The client can use the mechanism in [I-D.thomson-tls-care] to prompt
   the server to request a client certificate, to avoid the problem
   where the server doesn't know to make this request.

3.  Security Considerations

   Clients that support this authentication scheme will create a new
   connection each time that they see a challenge.  This could be
   exploited in order to generate additional load in terms of
   connections on both server and client.

   Using new connections for client authentication has additional
   processing costs to the client in proving access to the private keys
   associated with the client certificate; and to the server in proving
   access to the private keys associated with their certificate twice in
   the case that the client opts for confidentiality protection on the
   client certificate.

   HTTP/2 [I-D.ietf-httpbis-http2] allows clients to use the same
   connection for multiple canonical root URIs.  Certificate-based
   client authentication as defined by this specification is bound to a
   single origin.  This could create issues whereby the security
   properties of a connection could become confused.  Clients MUST
   ensure that a client-authenticated connection is only used for the
   origin for which it was created.

4.  IANA Considerations

   IANA is requested to create an entry in the HTTP Authentication
   Scheme Registry with the following information:

      ClientCertificate

      This document




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      This scheme does not rely on the Authorization header field.

5.  Acknowledgements

   Eric Rescorla helped identify the problem and formulate this
   mechanism.  Julian Reschke and Michael Koeller provided excellent
   feedback.

6.  References

6.1.  Normative References

   [I-D.ietf-httpbis-p7-auth]
              Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Authentication", draft-ietf-httpbis-p7-auth-26
              (work in progress), February 2014.

   [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.

   [RFC6454]  Barth, A., "The Web Origin Concept", RFC 6454, December
              2011.

6.2.  Informational References

   [I-D.ietf-httpbis-http2]
              Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer
              Protocol version 2", draft-ietf-httpbis-http2-12 (work in
              progress), April 2014.

   [I-D.thomson-tls-care]
              Thomson, M., draft-thomson-tls-care-00 (work in progress),
              March 2014.

Author's Address

   Martin Thomson
   Mozilla
   Suite 300
   650 Castro Street
   Mountain View, CA  94041
   US

   Email: martin.thomson@gmail.com




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