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

[Brian Campbell <[e-mail]>]

A few remarks/responses inline below this time...

On Wed, Apr 3, 2019 at 1:38 PM Vittorio Bertocci <Vittorio=
[e-mail]> wrote:

> Thanks guys for the comment, sorry for the delay in addressing them.
> I am not married to the claim types used in here, so if you think that
> reusing the ones in the id_token can cause confusion we should expand on
> the specific ways in which you think might go south.
>

My concern isn't with reusing the names/types of the claims per se.  But
more generally that codifying the use of certain authentication-centric
claims in the context of an access token furthers the potential confusion
around authentication vs. authorization that has been a nagging problem for
OAuth (i.e. the https://oauth.net/articles/authentication/ article).


However I think it's important that the information on say, whether the
> current token was obtained using MFA or a specific authentication factor is
> something that API developers can legitimately latch to when doing
> authorization decisions. From the perspective of a developer modeling a
> solution, whether functionality is delivered as a route in a postback based
> web app (hence receiving an id_token or derived) or as an API consumed by a
> native app, the business requirement gating access to that functionality
> doesn't change. If the admin managing that resource establishes that access
> should be performed only via MFA, the developer should be equipped to
> enforce that regardless of the stack used to expose functionality (web app,
> API).
> Although it is true that triggering the desired behavior might be achieved
> by the resource setting and contract with the AS, along the lines of what
> David said, it's actually not uncommon for those policies to be assigned on
> the resource AFTER the current session was established and/or the
> corresponding AT was obtained and cached. Furthermore, the requirement
> might be more granular than an AS policy can tolerate (an API might
> requires MFA only for certain routes, hence hard to express in a static
> policy) and triggered in form of challenges. So the situation in which you
> have an AT with the right issuer, audience, etc but was obtained with a
> policy now obsolete/unacceptable to the RP is strong. Requesting to support
> revocation just for this seems overkill, especially given that the scenario
> in which the same logical app is exposed as both web app and native
> client+API, the code consuming those claims is already in place. It just
> makes intuitive sense for developers.
> In summary, one can take steps to push as much of the MFA requirements to
> the AS settings for a particular request, but ultimately the desire of the
> API developer to enforce that it actually happened is a requirement I
> encountered often in practice. Anything providing extra context to refine
> decisions about it (like auth_time, which might inform decisions about
> whether to accept an MFA check occurred N minutes ago or refuse access).
>

I understand what you are saying but but personally do not find it
sufficiently compelling.  But that's just my opinion and not a hill I want
to die on (at the present time anyway).



> I thought that reusing the existing names for the same concepts just made
> sense (dev existing skills, existing codebases, etc etc) and especially in
> the case in which the values are exactly the same, and the idea seemed to
> receive good support during OSW.
>

Our recollection of OSW differs somewhat. As I recall there was support for
pointing to identity claims from OIDC for additional end-user info. But
there was some grumbling (from John and myself at least) at first mention
of acr/amr and auth_time. By the time it came up again near the end of the
last unconference session, I wasn't wanting to prolong things because I was
kinda worn out for the day and wanting to get to Frankfurt that evening
before sunset ('cause I like to do stuff like this:
https://flic.kr/p/2fiAaPe :) ).



> But I am completely open to change it of course, especially for cases like
> the one identified by George.
>

FWIW, to me, George's suggestion "assume[ing] that the auth_time value
should be updated to the latest time at which the user authenticated"
though some unspecified and in many cases non-existent link between the AT
and a current user session at the AS is an example of how
authentication-centric claims in an access token can be confusing.




> WDYT?
>
> On Wed, Apr 3, 2019 at 10:24 AM Brian Campbell <bcampbell=
> [e-mail]> wrote:
>
>> +1 to David's question here. I'd like to see justifying use cases (beyond
>> just the fact that some people are already doing it) for auth_time, acr,
>> and amr to be available in OAuth JWT access tokens. Those claims are
>> defined for, and in the context of, an ID Token and I fear that codifying
>> their use in an access token will lead to misuse and/or confusion.
>>
>> On Mon, Apr 1, 2019 at 1:03 PM David Waite <[e-mail]>
>> wrote:
>>
>>> Do we know if there is a justifying use case for auth_time, acr, and amr
>>> to be available in OAuth JWT access tokens? These are meant to be messages
>>> about the client, either directly (in the case of client credentials) or
>>> about its delegated authorization of the user.
>>>
>>> Embedding attributes about the user (such as group membership and roles)
>>> can be used for the resource to make finer-grained decisions than scopes,
>>> but normally I would expect say acr limitations enforced by a resource to
>>> instead be controlled by the AS requiring a higher quality authentication
>>> to release certain scopes.
>>>
>>> Thats of course not to say extensions to OAuth such as OIDC can’t
>>> provide these values, just that they might better be defined by those
>>> extensions.
>>>
>>> -DW
>>>
>>> On Apr 1, 2019, at 9:12 AM, George Fletcher <
>>> gffletch=[e-mail]> wrote:
>>>
>>> Thanks for writing this up. One comment on auth_time...
>>>
>>>    auth_time  OPTIONAL - as defined in section 2 of [OpenID.Core <https://tools.ietf.org/html/draft-bertocci-oauth-access-token-jwt-00#ref-OpenID.Core>].
>>>       Important: as this claim represents the time at which the end user
>>>       authenticated, its value will remain the same for all the JWT
>>>       access tokens issued within that session.  For example: all the
>>>       JWT access tokens obtained with a given refresh token will all
>>>       have the same value of auth_time, corresponding to the instant in
>>>       which the user first authenticated to obtain the refresh token.
>>>
>>>
>>> During a current session a user can be challenged for additional
>>> credentials or required to re-authenticate due to a number of different
>>> reasons. For example, OIDC prompt=login or max_age=NNN. In this context,
>>> I'd assume that the auth_time value should be updated to the latest time at
>>> which the user authenticated.
>>>
>>> If we need a timestamp for when the "session" started, then there could
>>> be a session_start_time claim.
>>>
>>> Thanks,
>>> George
>>>
>>> On 3/24/19 7:29 PM, Vittorio Bertocci 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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