Comments on draft-ietf-oauth-token-exchange-10

I propose the following rephrasing for sections 6 and 7:

6 . Security Considerations

All of the normal security issues that are discussed in [JWT],especially in relationship to comparing URIs and dealing with unrecognized values, also apply here.  In addition, both delegation and impersonation introduce unique security issues. Any time one user receives a token, the potential for abuse is a concern, since that user might be willing to collude with another user so that other user could use the token.

Techniques like the binding of an access token to a TLS channel described elsewhere are ineffective since the legitimate user would be able to perform all the cryptographic computations that the other user would need to demonstrate the ownership of the token. The use of the "scp" claim is suggested to mitigate potential for such abuse, as it restricts the contexts in which the token can be exercised. If the issued access token scope allows to unambiguously identify the user, then that user is likely to be reluctant to collude with another user. However, if the issued access token scope only indicates that the user is over 18, then there is no risk for the original user to be discovered and in such a context a collusion may easily take place. This document does not specify techniques to prevent such a collusion to be successful.

7 . Privacy Considerations

Tokens typically carry personal information and their usage in Token Exchange may reveal details of the target services being accessed. The resource and the audience parameters allow authorization servers to know where the issued access token will be used. This may be a privacy concern for some users. This document does not specify techniques to prevent authorization servers to know where the access tokens they issue will be used.

Denis
A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Web Authorization Protocol WG of the IETF.

         Title           : OAuth 2.0 Token Exchange
         Authors         : Michael B. Jones
                           Anthony Nadalin
                           Brian Campbell
                           John Bradley
                           Chuck Mortimore
        Filename        : draft-ietf-oauth-token-exchange-10.txt
        Pages           : 32
        Date            : 2017-11-30

Abstract:
    This specification defines a protocol for an HTTP- and JSON- based
    Security Token Service (STS) by defining how to request and obtain
    security tokens from OAuth 2.0 authorization servers, including
    security tokens employing impersonation and delegation.


The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-ietf-oauth-token-exchange/

There are also htmlized versions available at:
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https://datatracker.ietf.org/doc/html/draft-ietf-oauth-token-exchange-10

A diff from the previous version is available at:
https://www.ietf.org/rfcdiff?url2=draft-ietf-oauth-token-exchange-10


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