[Openid-specs-ab] Call for Adoption for the OpenID Connect Key Binding Specification

[Andrii Deinega]

Dick,

Do you consider a native OAuth client (which helps the ssh utility to
inject and forward an ID Token) and sshd (which retrieves and handles the
ID Token) to be two different components of the same RP?

If yes... I'm curious whether, in your opinion, the OP should be aware that
the ID Tokens it issues are actually being forwarded and used elsewhere.

It's really great to see a list of more or less concrete use cases in this
area (maybe... for a bit better transparency in this area).

Thank you.

All the best,
Andrii


On Mon, Sep 29, 2025 at 4:28 AM Dick Hardt <dick.hardt at gmail.com> wrote:

> I agree that the recipient of a JWT should reject it if it is not the
> intended audience.
>
> We think of the "other system" to be another component of the RP -- and
> because of that, that an id_token is the right token to bind and that both
> would verify the id_token has the correct "aud" value.
>
> VCs were designed for the issuer - holder - verifier model to protect the
> privacy of the user by preventing the issuer from learning about
> presentation by the holder to a verifier.
>
>
>
> On Fri, Sep 26, 2025 at 7:28 PM Andrii Deinega via Openid-specs-ab <
> openid-specs-ab at lists.openid.net> wrote:
>
>> I believe that any recipient of a JWT (in this case, an ID Token) should
>> immediately reject it if it isn't the intended audience (which is indicated
>> by the aud claim), regardless of whether cryptographic binding is present
>> or not. This alone makes the statement below too problematic for me.
>>
>> When an RP wants to prove to another system that it has authenticated a
>>> user, it may present the ID Token as a bearer token. However, bearer tokens
>>> are vulnerable to theft and replay attacks - if an attacker intercepts the
>>> ID Token, they can impersonate the authenticated user to downstream systems
>>> that accept a ID Token as a bearer token.
>>
>>
>> It's difficult to imagine multiple systems (recipients) sharing the same
>> value in the aud claim (this value must be a client_id of the RP per the
>> Core spec). It's fair to add the aud claim may contain an array with more
>> than one element, but it's also fair to say this practice is discouraged
>> (1) and comes with additional complexity and concerns (2).
>>
>> At the end of the day... I see a lot of value, and I see the reason why
>> people want to have the standard around "proving to another system that it
>> has authenticated a user," but I don't think that repurposing existing ID
>> Tokens for it is the right way to go.... I’d suggest, and actually love to
>> see - the use of SD JWT VCs (or other VCs) for this purpose instead.
>>
>> I haven’t reached the point where I need to "touch" Justin’s concerns...
>> I fully agree with him on them.
>>
>> All the best,
>> Andrii
>>
>> On Fri, Sep 26, 2025 at 9:05 AM Justin Richer via Openid-specs-ab <
>> openid-specs-ab at lists.openid.net> wrote:
>>
>>> I do not support adoption of this work. The ID Token is not intended to
>>> be a conveyable artifact, and using it as such is a security layer
>>> boundary. It’s hard enough to get people to not use ID Tokens as Access
>>> Tokens today, since a lot of developers see all JWTs as equivalent, really.
>>> This work would make this problem significantly worse.
>>>
>>>  — Justin
>>>
>>> On Sep 15, 2025, at 6:57 PM, Michael Jones via Openid-specs-ab <
>>> openid-specs-ab at lists.openid.net> wrote:
>>>
>>> This starts a two-week call for feedback on whether to adopt the OpenID
>>> Connect OpenID Connect Key Binding specification contributed to the working
>>> group by Dick Hardt and Ethan Heilman as an OpenID Connect Working Group
>>> specification.  Please reply-all by Monday, September 29, 2025 saying
>>> whether you are favor of adoption or not, also saying why.
>>>
>>> The specification was contributed at
>>> https://lists.openid.net/pipermail/openid-specs-ab/2025-August/010890.html.
>>> It has been extensively discussed by the working group both on calls and on
>>> the mailing list.  From my observations of the discussion as a working
>>> group chair, I believe that there is consensus that it would be useful to
>>> have a standard solving the problem addressed by this specification.
>>>
>>>                                                 Writing as a working
>>> group chair,
>>>                                                                 -- Mike
>>>
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