Re: [OAUTH-WG] Web Authorization Protocol (oauth) WG Virtual Meeting: 2020-04-13

Why does the "sub" need to be required?

An access token is to prove authorization. The RS may not need "sub" to
constrain fulfilling the client request.

For example, it the access token has the same properties as a movie ticket,
the RS does not need to have any identifier for who purchased the movie
ticket.

The privacy implication is the RS can correlate across API calls to know it
is the same subject.

On Mon, Apr 13, 2020 at 8:16 AM Denis <denis.ietf@free.fr> wrote:

> Hello,
>
> More on privacy about "JWT Profile for Access Tokens".
>
> The current document REQUIRES the claim names *sub* and *client_id*.
>
>    - sub  REQUIRED - as defined in section 4.1.2 of [RFC7519].
>    - client_id  REQUIRED - as defined in section 4.3 of [RFC8693]
>
> *1) **sub  REQUIRED*
>
> RFC 7519 states:
>
> 4.1.2.  "sub" (Subject) Claim
>    The "sub" (subject) claim identifies the principal that is the
>    subject of the JWT.  The claims in a JWT are normally statements
>    about the subject.  The subject value MUST either be scoped to
>    *be locally unique in the context of the issuer or be globally unique*.
>    The processing of this claim is generally application specific.  The
>    "sub" value is a case-sensitive string containing a StringOrURI
>    value.  *Use of this claim is OPTIONAL.*
>
> If *sub *is *REQUIRED *for this profile, then this allows all resource
> servers to link accesses made by the same client on different servers.
>
> *2) client_id  REQUIRED*
>
> RFC 8693 states:
>
> 4.3. "client_id" (Client Identiﬁer) Claim
> The client_id claim carries the client identiﬁer of the OAuth 2.0 [RFC
> 6749] client that requested the token.
>
> RFC 6749 states:
>
> 2.2.  Client Identifier
>    The authorization server issues the registered client a client
>    identifier -- a unique string representing the registration
>    information provided by the client.  The client identifier is not a
>    secret; it is exposed to the resource owner and MUST NOT be used
>    alone for client authentication.  *The client identifier is unique to*
> *   the authorization server.*
>
> If *client_id* is REQUIRED for this profile, this also allows all
> resource servers to link accesses made by the same client on different
> servers.
>
> *Both claim names should be OPTIONAL *to allow to support the privacy
> principle of unlinkability.
>
> Would both names remain *REQUIRED*, the Privacy considerations section
> should mention that such a linkage by different resource servers
> will always be possible when using this profile.
>
> Denis
>
> I have uploaded the second presentation for today's session, the JWT
> Profile for Access Tokens.
> https://datatracker.ietf.org/meeting/interim-2020-oauth-04/session/oauth
>
> Regards,
>  Rifaat
>
>
>
> _______________________________________________
> OAuth mailing list
> OAuth@ietf.org
> https://www.ietf.org/mailman/listinfo/oauth
>