[Openid-specs-ab] [openid/connect] Messages - Add 'prn' claim to id_token to support JWT Assertion (issue #687)

Tue Dec 18 23:00:24 UTC 2012

Dale, there's a thread about adding the "aud":[list] syntax to JWT on the OAuth list (where JWT is actually being defined) right now.  See http://www.ietf.org/mail-archive/web/oauth/current/msg10285.html.  I'd suggest joining the list at https://www.ietf.org/mailman/listinfo/oauth and sending a note supporting this addition.  I'd be sure to point out that you're already using it in practice.

That would help move the discussion along on that topic.

                                                                Thanks,
                                                                -- Mike

From: openid-specs-ab-bounces at lists.openid.net [mailto:openid-specs-ab-bounces at lists.openid.net] On Behalf Of Dale Olds
Sent: Tuesday, December 18, 2012 2:38 PM
To: Brian Campbell
Cc: <openid-specs-ab at lists.openid.net>
Subject: Re: [Openid-specs-ab] [openid/connect] Messages - Add 'prn' claim to id_token to support JWT Assertion (issue #687)

Hey Brian,

To your question: yes, regular access tokens. We follow a convention of RS.CoarsePermission in defining scopes. So if a user delegated to a client authorization to read their openid info, modify their resources on the cloud controller, and read users and groups on their behalf -- we *could* combine that in single token (not that that's a good idea). The oauth2 scope would look like "openid cloud_controller.write scim.read". The JWT access token would contain "aud":["openid","cloud_controller","scim"]. Such a token could be presented to the oidc /userinfo endpoint, the scim /Users and /Groups endpoints, and the cloud_controller endpoints. Each endpoint validates the token and verifies that it is in the intended audience list. This approach had been quite useful and flexible. The downside is that we are not completely insulating the RSs from each other. In our case we never actually combine user account management with cloud controller access and since the services are all in the same management domain and we felt potential abuse was low when sharing access to the openid /userinfo.

IIRC we made some of our implementation choices due to a comment from Mike Jones that (from memory) went something like this: while 'aud' or other JWT claims are each single claims the J stands for JSON, so an array is a fine value. Made sense to me. Therefore our tokens look like your last example of "aud":["Dale","Brian"].

--Dale
On 12/17/2012 07:52 AM, Brian Campbell wrote:
You're right Dale, there's nothing that says it can only be a single principal. But aud's current definition as a single StringOrURI value does mean that identifying more than one principal would have to be done by somehow encoding that fact into a single value. Maybe a value that represents a group or some delimiter or something. But interpretations of that that kind of thing seem likely to be very application specific. And some specs might have restrictions/requirements that make that kind of thing difficult too - like Connect specifies that the aud of the ID Token be the client id of the client/RP.

You say you commonly generate JWTs that have an RS and the AS identified in the audience. I assume those are regular access tokens? What does that look like?

Trying to explain what I'm thinking a bit more, by way of example, if we wanted to produce a JWT that indicated either you or I as an intended audience, we'd have to do something like "aud":"DaleOrBrian" or "aud":"some-group-identifier" where some-group-identifier indicates a group that we both understand and consider ourselves part of.

I'm wondered if this kind of thing is common enough that the JWT should try and help accommodate it by allowing for multiple values to be present in the aud claim as an array and stating that the consumer of the JWT must identify itself with one of those values. So a token sent to either you our I might have an audience claim that looks like, "aud":["Dale", "Brian"].

On Sat, Dec 15, 2012 at 1:53 PM, Dale Olds <olds at vmware.com<mailto:olds at vmware.com>> wrote:
Somewhat tangentally though is that JWT only allows for a single audience to be identified in the token.

On reading Brian's note I reread the 'aud' section in the JWT spec. It is a single 'aud' claim but and I don't see it as being limited to a single principal. It says the principal processing the token must be identified in the claim and that the interpretation is application specific, but I don't see a limit of one. It does add a lot of flexibility to specify more than one -- which could be good or bad -- and we do so in our implementation. We commonly generate JWTs that have an RS and the AS identified in the audience. If it could also help in the OIDC cases, I think that could be an option. Or did I miss something in the JWT spec?

--Dale

On 12/14/2012 03:11 PM, Brian Campbell wrote:
That's one way to go.

The assertion drafts are mostly about using the assertion to cross organizational boundaries (though I guess not necessarily). Some trusted party issues an assertion and says who it's for. The consumer of the assertion makes sure it was intended for them.  This seems is a special case of that where the issuer is also one of the indented audiences.   The SAML draft would allow this situation by allowing for more than one acceptable audience to be included in the token (but you can't do that in JWT). And I'm not aware of anyone actually doing that kind of thing in practice with SAML now. I'm not sure it's the right way to approach it for that matter.

Alternatively the AS could have some special condition on audience validation for tokens that it issued itself. That's a pattern I've heard suggested several times before for various things but, though I can't say exactly why, I've never been real fond of it.

I'm not sure exactly what should be done with the case you describe.

Somewhat tangentally though is that JWT only allows for a single audience to be identified in the token. I've been wondering to myself for some time now if that's too restrictive. Being able to indicated more than one intended audience in a token seems like it would add a lot of flexibility to a number of these various token exchange type scenarios. But then again SAML has that and I don't know how much it gets utilized. So maybe it would just be adding unneeded complexity.

I'm going to stop rambling now...

On Fri, Dec 14, 2012 at 3:40 PM, Justin Richer <jricher at mitre.org<mailto:jricher at mitre.org>> wrote:
You are correct. I hadn't caught that, but it does state in JWT Assertions:
The JWT MUST contain an aud (audience) claim containing a URI reference that identifies the authorization server, or the service provider principal entity of its controlling domain, as an intended audience. The token endpoint URL of the authorization server MAY be used as an acceptable value for an aud element. The authorization server MUST verify that it is an intended audience for the JWT.

Which doesn't leave much wiggle room for the OIDC interpretation. Between this an 'prn', maybe this is a different kind of assertion claim, then? An id-token assertion grant type?

 -- Justin

On 12/14/2012 04:51 PM, Brian Campbell wrote:
I believe the current wording of the specs would prohibit that.

On Fri, Dec 14, 2012 at 2:10 PM, Justin Richer <jricher at mitre.org<mailto:jricher at mitre.org>> wrote:
My original idea is for the Client to use the JWT Assertion flow with a current id_token to refresh it and get a new id_token. This goes back to the session management proposal linked to within the issue. In this case, the audience for the token really *is* the client, and an AS will need to look for that.

 -- Justin

On 12/14/2012 04:04 PM, Brian Campbell wrote:
I had a comment/question related to the below comment on issue 687 but not really related to the issue itself. So figured the list would be the best forum.

Regarding the potential use of an ID Token as an assertion in the OAuth JWT Assertion Profile - aren't the requirements around the "aud" claim also potentially a problem?

Connect says the aud of an ID Token "MUST be the OAuth 2.0 client_id of the Client." While the OAuth JWT Assertion Profile is a little more flexible but basically says the aud must identify the AS or its controlling entity. Doesn't this imply that an ID Token could only really be used to get an access token within the scope of the client to whom it was sent in the first place? Which doesn't seem very useful. Or is it?

On Thu, Dec 13, 2012 at 5:23 PM, Michael Jones <issues-reply at bitbucket.org<mailto:issues-reply at bitbucket.org>> wrote:
--- you can reply above this line ---

Issue 687: Messages - Add 'prn' claim to id_token to support JWT Assertion
https://bitbucket.org/openid/connect/issue/687/messages-add-prn-claim-to-id_token-to
Michael Jones:

I agree that it would be a shame, architecturally, if we can't use an ID Token as a assertion in a way that complies with the OAuth JWT Assertion Profile.  I believe we need to address this.

There are few ways to do this, as I see it:

1.  Add "prn" to the ID Token.  Upside:  Simple.  Downsides:  Wastes space through duplication of data; potential interop problem where not everyone duplicates or uses the information in the same way.

2.  Replace "user_id" with "prn" in the ID Token.  Downside:  Less mnemonic than user_id.  Upside:  simple.

3.  Modify the OAuth JWT Assertion Profile to allow the subject to be identified by a claim other than "prn" - possibly explicitly calling out "user_id".  Upside:  would work.  Downside:  Codifies inconsistency.

4.  Replace both "user_id" and "prn" with a different claim in both specs.  Candidates include "id" and "sub".

Let's make this a topic for Monday's call.

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