Network Working Group                                          J. Schaad
Internet-Draft                                            August Cellars
Intended status: Experimental                           October 22, 2018
Expires: April 25, 2019


            Use of a CWT identifier as a Confirmation Method
                       draft-schaad-cnf-cwt-id-00

Abstract

   TBD

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  CWT Id Confirmation Method  . . . . . . . . . . . . . . . . .   3
   4.  CWT Id in AS Response . . . . . . . . . . . . . . . . . . . .   3
   5.  Processing Rules for the Issuer of a CWT Id Confirmation
       Method  . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Processing Rules for the CWT Id Confirmation Method . . . . .   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   In many cases an authorization in the form of a COSE Web Token (CWT)
   [RFC8392] will be issued in the ACE OAuth [I-D.ietf-ace-oauth-authz]
   framework with a minimal set of privileges and a Proof-of-Possession
   claim [I-D.ietf-ace-cwt-proof-of-possession].  It may then become
   necessary to issue a new token for a shorter period with more
   capabilities, but use the same information for validation.  In these
   cases it makes sense to issue a new authorization token which refers
   the the first token to provide the additional capabilities.  This
   document defines a new confirmation type that allows this type of
   referencing to be done.

   This differs from the refresh token in that the new token will be
   limited to the duration of the existing CWT, while a new POP CWT
   would be issued when using a refresh token.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Terminology

   o  "Relying Party" is used in this document to refer to the party
      which is relying on the contents of a CWT in order to make a
      security decision.  In other OAuth documents, this is normally
      referred to as the XXXXXX.





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   o  "Referenced CWT" is used to denote the CWT which is referred to or
      referenced by a referencing CWT.  The referenced CWT has a
      confirmation type with the POP keying information in it.

   o  "Referencing CWT" is used to denote the CWT which is making a
      reference to a second CWT.  The referencing CWT contains the
      confirmation type defined in this document.

3.  CWT Id Confirmation Method

   The CWT Id confirmation method is identified by TBD1 in the 'cnf'
   element (defined in [I-D.ietf-ace-cwt-proof-of-possession].  For use
   in documentation the string value of 'cwtid' is to be used to refer
   to this confirmation type.

   The CWT Id confirmation method uses the type of CBOR map and has the
   following fields:

   o  Issuer is an optional field in the map.  If present the issuer
      field contains the 'iss' field of CWT which is being referenced.
      If absent, the issuer is the same entity which issued the
      referencing CWT.  When encoded, this field uses TBD2 as the map
      key.

   o  CWT Id is a required field in the map.  The field contains the
      'cwtid' field of the referenced CWT.  When encoded, this field
      uses TBD3 as the map key.

   An example of what this would look like is:

   / cnf /: {
       / cwtid /: 'CWTID 1234',
       / iss /: "Entry-Level AS"
   }

4.  CWT Id in AS Response

   Since the CWT Id is currently only provided to the RS as part of the
   token, for an AS which supports this option the CWT Id additionally
   needs to be provided to the Client.  This document therefore defines
   two new fields to go into C-AS response messages:

      "iss" provides the issuer name of the CWT.  This field is only
      present for an AS which would allow a second AS to refer to the
      CWT.

      "cwtid" contains the CWT Id for the issued token.




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5.  Processing Rules for the Issuer of a CWT Id Confirmation Method

   When an AS is going to issue a CWT it MUST perform the following
   steps or their equivalent:

   1.  If the issued CWT will refer to a CWT issued by a different AS,
       the issuing AS MUST be configured to permit this.

   2.  The AS MUST validate that the entity for which this CWT is being
       issued for is the same entity that is the subject of the
       referenced CWT.  This can be done by causing the client to
       perform a POP operation with the referenced CWTs POP key
       information or by querying the AS which issued the referenced
       CWT.  If the same AS is being used for both CWTs, then the AS can
       consult a database of clients and CWTs to check for identity
       matching.

   3.  The issued CWT should refer to the original POP CWT.  The chain
       of trust SHOULD NOT be transitive through another CWT.

6.  Processing Rules for the CWT Id Confirmation Method

   When a relying party receives a referencing CWT it MUST perform the
   following steps or their equivalent as part of making a security
   decision:

   1.  The referencing CWT MUST have the authentication checked on it.
       If the authentication fails, the CWT MUST be rejected.

   2.  If the CWT Id confirmation type contains an issuer field,
       configuration information MUST be checked that the referencing
       CWT issuer is permitted to use the referenced CWT issuer.  If the
       reference is not permitted, then the CWT MUST be rejected.

   3.  If the referenced CWT is expired, the referencing CWT MUST be
       rejected.

   4.  The claims in the referenced CWT are copied from the referenced
       CWT to the referencing CWT if the claim does not exist in the
       referencing CWT.

   5.  The modified CWT is then processed in a normal manner.

7.  Security Considerations

   As the security of the set of CWTs is going rest on the underlying
   POP CWT, loss of the key will allow any CWT which references the




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   orignal CWT to be used by a third party.  All entities which have the
   secret portion of the key need to protect that portion of the key.

   The use of this feature assumes a specific model of evaluating the
   rules for access control.  Specifically, it assumes that if there are
   multiple access tokens, satisfying the conditions for any of the
   tokens means that access is going to be granted.  This model is in
   contrast to one where if any of the access tokens was a deny, then
   access to to the resource would be denied.

8.  IANA Considerations

   There are some items that need to be registered.  Figure out what
   they are and put them here.

9.  Normative References

   [I-D.ietf-ace-cwt-proof-of-possession]
              Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
              Tschofenig, "Proof-of-Possession Key Semantics for CBOR
              Web Tokens (CWTs)", draft-ietf-ace-cwt-proof-of-
              possession-03 (work in progress), June 2018.

   [I-D.ietf-ace-oauth-authz]
              Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
              H. Tschofenig, "Authentication and Authorization for
              Constrained Environments (ACE) using the OAuth 2.0
              Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-16
              (work in progress), October 2018.

   [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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8392]  Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
              "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
              May 2018, <https://www.rfc-editor.org/info/rfc8392>.

Author's Address







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   Jim Schaad
   August Cellars

   Email: ietf@augustcellars.com















































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