Re: [OAUTH-WG] draft-bertocci-oauth-access-token-jwt-00

["Schanzenbach, Martin" <[e-mail]>]

I agree. Maybe RFC 7519 is actually as good as it gets wrt claim specifications?
At least for OAuth. Use case specific profiles can/must then use their own definitions (see OIDC) for (JWT) ATs.
I mean, at least for OIDC, an AT which is the result of a client credential grant isn't even a thing which really simplifies the specification of a JWT AT in OIDC.

So maybe just reference / rely on RFC 7519 for the basic claims and clarify usage of this JWT using the typ?

> On 4. Apr 2019, at 18:29, Hans Zandbelt <[e-mail]> wrote:
> 
> I believe the root problem is that we're trying to unify across tokens that are issued for different use cases (auth vs. authz), different subjects and different audiences. The JWT spec allows us to cover those use cases nicely within its own semantics but the profile specific use case semantics are really different at heart. This problem becomes even more apparent in SPAs that share both the id_token and the access_token across frontend and backend: the RS then needs to flip back and forth between the use cases and their specific semantics.
> 
> It seems were stuck between a rock and a hard place: I don't think there's a way to make things explicit and clear across use cases whilst sticking with JWT semantics only (as clear as the semantics may be in their own RFC7519 context). I also don't think there's a way to make things explicit and clear without breaking existing deployments and existing spec text which is as awkward.
> 
> Hans.
> 
> On Thu, Apr 4, 2019 at 5:58 PM Schanzenbach, Martin <[e-mail]> wrote:
> I think what needs to be clarified is whether the "sub" claim should denote the caller (=client) or the RO in the case of an JWT AT.
> RFC 7519 only defines "sub" to be the principal which is the subject of all claims in the JWT.
> This means that the AT can contain either claims regarding the client OR the RO, but not both. (I prefer to use RO instead of user as I think this a term better used in OIDC).
> 
> Now, the question is what does an RS need to make an authorisation decision? Claims about the client or claims about the RO?
> Since OIDC already has ID Tokens as JWT which have the RO as "sub", maybe it makes sense to have the client as sub for the AT?
> If the RS needs claims about the RO in order to do authorization decisions, maybe it needs to be presented with an ID Token (which would imply that it is issued with the RS in its aud claim).
> 
> > On 4. Apr 2019, at 17:50, George Fletcher <gffletch=[e-mail]> wrote:
> >
> > The more I think about this the more I land in the "No" camp.
> >
> > The subject of a token should be the principal of that token. It shouldn't matter whether that is a machine, a user, or a device. Trying to separate out "humans" as a special class will just make things more complicated. If we need a claim to identify the subject is a "human" then why not just add that. This doesn't break anything and makes it easy for people to detect this case in those use cases where it's required.
> >
> > Thanks,
> > George
> >
> > On 4/3/19 4:56 PM, Hans Zandbelt wrote:
> >> I will argue that in a way such deployments are already broken e.g. in the typical use case of onboarding client accounts in the same directory/OU/namespace as user accounts and we don't need to cater for that.
> >>
> >> Hans.
> >>
> >> On Wed, Apr 3, 2019 at 10:48 PM George Fletcher <[e-mail]> wrote:
> >> I agree that this will break a lot of existing flows... especially those using any form of the client_credentials flow. In that sense I'm not completely on board yet :)
> >>
> >> On 3/26/19 12:56 PM, Hans Zandbelt wrote:
> >>> great summary! this will hurt quite a few existing m2m deployments but I do like the rigidness of it all: it is very explicit, cannot misinterpreted and thus prevents failure (which is really what Dominick is after); I'm on board
> >>>
> >>> Hans.
> >>>
> >>> On Tue, Mar 26, 2019 at 5:49 PM Vittorio Bertocci <Vittorio=[e-mail]> wrote:
> >>> thank you Steinar and everyone else for the comments on this!
> >>> To summarize the situation so far: Dominick, Steinar, Rob, David, Nov, Bertrand recommend using sub only for users. Martin would like to have the sub for app only flows as well. Hans is neutral.
> >>> That does sound like the sub as user has more consensus, tho before changing it I'd wait for the people currently at IETF104 to have more time to comment as well.
> >>> Clarification. If the goal is to be able to apply the logic "if there's a sub, it's a user flow", we have to explicitly disallow (MUST NOT) the use of sub when that's not the case. Are all OK with it?
> >>>
> >>> Dave, the suggestion of having explicit typing for app only vs user only is interesting! For the purpose of putting together an interoperable profile, tho, I would suggest we table it for v1 in the interest of getting to something easy to adopt (hence with small delta vs existing implementations) faster.
> >>>
> >>> On Tue, Mar 26, 2019 at 1:40 AM Steinar Noem <[e-mail]> wrote:
> >>> Hi Vittorio, we  (the national federation-gateway for the health services in norway - "HelseID")  think his is a really valuable initiative!
> >>> We also agree with Dominick concerning definition of the "sub" claim.
> >>>
> >>> <mvh>Steinar</mvh>
> >>>
> >>> tir. 26. mar. 2019 kl. 07:25 skrev Dominick Baier <[e-mail]>:
> >>> From an access token consumer (aka API) developer point of view, I prefer this logic
> >>>
> >>> "If sub is present - client acts on behalf of a user, if not - not."
> >>>
> >>> Anything more complicated has a potential of going wrong.
> >>>
> >>>
> >>> On 26. March 2019 at 01:34:53, Nov Matake ([e-mail]) wrote:
> >>>
> >>>> Hi Vittorio,
> >>>>
> >>>> Yeah, I’m concerning user & client ids collision.
> >>>> I haven’t seen such implementations, but user-select username as sub, or incremental integer as sub & client_id will be easily collide.
> >>>>
> >>>> If you can enforce collision resistant IDs between user & client instances, it’ll works fine. I feel its overkill though.
> >>>>
> >>>> Sent from my iPhone
> >>>>
> >>>> On Mar 26, 2019, at 8:51, Vittorio Bertocci <[e-mail]> wrote:
> >>>>
> >>>>> Hey Nov, Dominick, Hans-
> >>>>> thanks for the comments. That was an area I was expecting to cause more discussion, and I am glad we are having this opportunity to clarify.
> >>>>> The current language in the draft traces the etymology of sub to OpenID Connect core, hence Dominick observation is on point. However in the description I express something in line with 7519, which was in fact my intent.
> >>>>>
> >>>>> The idea was to provide an identifier of the calling subject that is guaranteed to be present in all cases- this would allow an SDK developer to use the same code for things like lookups and membership checks regardless of the nature of the caller (user in a delegated case, app in app-only grants). The information to discriminate between user and app callers is always available in the token (say, the caller is a user if sub!=client_id, where client_id is always guaranteed to be present as well) hence there's no loss in expressive power, should that difference be relevant for the resource server.
> >>>>>
> >>>>> Dominick, Hans- I probably missed the security issue you guys are thinking of in this case. Of course, if this would introduce a risk I completely agree it should be changed- I'd just like to understand better the problem. Could you expand it in a scenario/use case to clarify the risk?
> >>>>> Nov- playing this back: is the concern that a user and a client might have the same identifier within an IDP? When using collision resistant IDs, as it is usually the case, that seems to be a remote possibility- did you stumble in such scenario in production?
> >>>>>
> >>>>> Thanks
> >>>>> V.
> >>>>>
> >>>>>
> >>>>> On Mon, Mar 25, 2019 at 7:44 AM Hans Zandbelt <[e-mail]> wrote:
> >>>>> I believe there are plenty of OAuth 2.0 only use cases out there... but nevertheless I agree with the potential confusion and thus security problems arising from that (though one may argue the semantics are the same).
> >>>>>
> >>>>> Hans.
> >>>>>
> >>>>> On Mon, Mar 25, 2019 at 3:39 PM Dominick Baier <[e-mail]> wrote:
> >>>>> Yes I know - and I think in hindsight it was a mistake to use the same claim type for multiple semantics.
> >>>>>
> >>>>> All the “this is OIDC not OAuth” arguments are making things more complicated than they need to be - in my experience almost no-one (that I know) does OIDC only - nor OAuth only. They always combine it.
> >>>>>
> >>>>> In reality this leads to potential security problems - this spec has the potential to rectify the situation.
> >>>>>
> >>>>> Dominick
> >>>>>
> >>>>> On 25. March 2019 at 14:58:56, Hans Zandbelt ([e-mail]) wrote:
> >>>>>
> >>>>>> Without agreeing or disagreeing: OIDC does not apply here since it is not OAuth and an access token is not an id_token.
> >>>>>> The JWT spec says in https://tools.ietf.org/html/rfc7519#section-4.1.2:
> >>>>>>
> >>>>>> "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"
> >>>>>>
> >>>>>> which kind of spells "client" in case of the client credentials grant but I also do worry about Resource Servers thinking/acting only in terms of users
> >>>>>>
> >>>>>> Hans.
> >>>>>>
> >>>>>> On Mon, Mar 25, 2019 at 2:41 PM Dominick Baier <[e-mail]> wrote:
> >>>>>> IMHO the sub claim should always refer to the user - and nothing else.
> >>>>>>
> >>>>>> OIDC says:
> >>>>>>
> >>>>>> "Subject - Identifier for the End-User at the Issuer."
> >>>>>>
> >>>>>> client_id should be used to identify clients.
> >>>>>>
> >>>>>> cheers
> >>>>>> Dominick
> >>>>>>
> >>>>>> On 25.. March 2019 at 05:13:03, Nov Matake ([e-mail]) wrote:
> >>>>>>
> >>>>>>> Hi Vittorio,
> >>>>>>>
> >>>>>>> Thanks for the good starting point of standardizing JWT-ized AT.
> >>>>>>>
> >>>>>>> One feedback.
> >>>>>>> The “sub” claim can include 2 types of identifier, end-user and client, in this spec.
> >>>>>>> It requires those 2 types of identifiers to be unique each other in the IdP context.
> >>>>>>>
> >>>>>>> I prefer omitting “sub” claim in 2-legged context, so that no such constraint needed.
> >>>>>>>
> >>>>>>> thanks
> >>>>>>>
> >>>>>>> nov
> >>>>>>>
> >>>>>>>> On Mar 25, 2019, at 8:29, Vittorio Bertocci <vittorio.bertocci=[e-mail]> wrote:
> >>>>>>>>
> >>>>>>>> Dear all,
> >>>>>>>> I just submitted a draft describing a JWT profile for OAuth 2.0 access tokens. You can find it in https://datatracker.ietf.org/doc/draft-bertocci-oauth-access-token-jwt/.
> >>>>>>>> I have a slot to discuss this tomorrow at IETF 104 (I'll be presenting remotely). I look forward for your comments!
> >>>>>>>>
> >>>>>>>> Here's just a bit of backstory, in case you are interested in how this doc came to be. The trajectory it followed is somewhat                                                           unusual.
> >>>>>>>>        • Despite OAuth2 not requiring any specific format for ATs, through the years I have come across multiple proprietary solution using JWT for their access token. The intent and scenarios addressed by those solutions are mostly the same across vendors, but the syntax and interpretations in the implementations are different enough to prevent developers from reusing code and skills when moving from product to product.
> >>>>>>>>        • I asked several individuals from key products and services to share with me concrete examples of their JWT access tokens (THANK YOU Dominick Baier (IdentityServer), Brian Campbell (PingIdentity), Daniel Dobalian (Microsoft), Karl Guinness (Okta) for the tokens and explanations!).
> >>>>>>>> I studied and compared all those instances, identifying commonalities and differences.
> >>>>>>>>        • I put together a presentation summarizing my findings and suggesting a rough interoperable profile (slides: https://sec.uni-stuttgart.de/_media/events/osw2019/slides/bertocci_-_a_jwt_profile_for_ats.pptx ) - got early feedback from Filip Skokan on it. Thx Filip!
> >>>>>>>>        • The presentation was followed up by 1.5 hours of unconference discussion, which was incredibly valuable to get tight-loop feedback and incorporate new ideas. John Bradley, Brian Campbell Vladimir Dzhuvinov, Torsten Lodderstedt, Nat Sakimura, Hannes Tschofenig were all there and contributed generously to the discussion. Thank you!!!
> >>>>>>>> Note: if you were at OSW2019, participated in the discussion and didn't get credited in the draft, my apologies: please send me a note and I'll make things right at the next update.
> >>>>>>>>        • On my flight back I did my best to incorporate all the ideas and feedback in a draft, which will be discussed at IETF104 tomorrow. Rifaat, Hannes and above all Brian were all super helpful in negotiating the mysterious syntax of the RFC format and submission process.
> >>>>>>>> I was blown away by the availability, involvement and willingness to invest time to get things right that everyone demonstrated in the process. This is an amazing community.
> >>>>>>>> V.
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> >>> Steinar Noem
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> 
> Martin Schanzenbach
> Fraunhofer AISEC
> Department Service & Application Security
> Parkring 4, 85748 Garching near Munich (Germany)
> Tel: [phone]
> [e-mail]
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Martin Schanzenbach
Fraunhofer AISEC
Department Service & Application Security
Parkring 4, 85748 Garching near Munich (Germany)
Tel: [phone]
[e-mail]
GPG: 6665201EA9257CC68FDE77E884335131EA3DABF0