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

[Steinar Noem <[e-mail]>]

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
>>>>    <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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>>>
>>>
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>>
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-- 
Vennlig hilsen

Steinar Noem
Partner Udelt AS
Systemutvikler

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