[Openid-specs-ab] Key-binding and dpop scope

[Kosuke Koiwai]

Can we separate the spec to add cnf to id_token and how to ask for it?

As I asked before, I want to add the key info to id_token, and the key is
the same as the one used for attestation-based client auth.

https://lists.openid.net/pipermail/openid-specs-ab/2025-August/010892.html

I want to add the cnf claim at the discretion of IdP, so RP doesn’t have to
add any to the scope.

Kosuke


On Sat, Aug 30, 2025 at 19:07 Dick Hardt via Openid-specs-ab <
openid-specs-ab at lists.openid.net> wrote:

> "bound_key" is crisper and says what is wanted in the token rather than
> what is to be done
>
> On Fri, Aug 29, 2025 at 6:51 PM Dag Helge Østerhagen via Openid-specs-ab <
> openid-specs-ab at lists.openid.net> wrote:
>
>> +1 for both "key_binding" and "cnf". Sigh.
>>
>> /dag
>> ------------------------------
>> *From:* Dick Hardt <dick.hardt at gmail.com>
>> *Sent:* Friday, August 29, 2025 7:47:45 PM
>> *To:* Artifact Binding/Connect Working Group <
>> openid-specs-ab at lists.openid.net>
>> *Cc:* Dag Helge Østerhagen <dag at udelt.no>; george at practicalidentity.com <
>> george at practicalidentity.com>; Filip Skokan <panva.ip at gmail.com>
>> *Subject:* Re: [Openid-specs-ab] Key-binding and dpop scope
>>
>> `key_binding` as scope name?
>>
>> On Fri, Aug 29, 2025 at 6:35 PM Dag Helge Østerhagen via Openid-specs-ab <
>> openid-specs-ab at lists.openid.net> wrote:
>>
>> Well,  currently the dpop header is used to signal token binding (and
>> inclusion of the cnf claim) for access and refresh tokens.   I don't see
>> any other use cases in the (near) future.
>>
>> /dag
>> ------------------------------
>> *From:* george at practicalidentity.com <george at practicalidentity.com>
>> *Sent:* Friday, August 29, 2025 7:01:54 PM
>> *To:* Artifact Binding/Connect Working Group <
>> openid-specs-ab at lists.openid.net>
>> *Cc:* Dag Helge Østerhagen <dag at udelt.no>
>> *Subject:* Re: [Openid-specs-ab] Key-binding and dpop scope
>>
>> My thought is that might depend on whether the ‘cnf’ scope is only
>> applied to the id_token or whether cnf claims should be added to other
>> issued tokens as well. Currently the proposed key-binding spec is specific
>> to id_tokens.
>>
>> George Fletcher
>> Identity Standards Architect
>> Practical Identity LLC
>>
>>
>>
>> On Aug 29, 2025, at 12:56 PM, Dag Helge Østerhagen via Openid-specs-ab <
>> openid-specs-ab at lists.openid.net> wrote:
>>
>> I like «id_token_cnf», but wouldn’t just «cnf» be more aligned with other
>> oidc scopes?
>>
>> /dag
>> ------------------------------
>> *From:* Openid-specs-ab <openid-specs-ab-bounces at lists.openid.net> on
>> behalf of george--- via Openid-specs-ab <openid-specs-ab at lists.openid.net
>> >
>> *Sent:* Friday, August 29, 2025 6:14:16 PM
>> *To:* Dick Hardt <dick.hardt at hello.coop>
>> *Cc:* george at practicalidentity.com <george at practicalidentity.com>;
>> Artifact Binding/Connect Working Group <openid-specs-ab at lists.openid.net>
>> *Subject:* Re: [Openid-specs-ab] Key-binding and dpop scope
>>
>> That makes sense to me; including ‘cnf’ in the scope name. Would we ever
>> want to allow the “key binding” mechanism to use something other than DPoP?
>> If so, and the express purpose is to provide key binding for the id_token,
>> then I’d recommend something like ‘id_token_cnf’.  It’s specific, clear and
>> doesn’t preclude methods other than DPoP to provide the necessary data for
>> the cnf claim.
>>
>> George Fletcher
>> Identity Standards Architect
>> Practical Identity LLC
>>
>>
>>
>> On Aug 29, 2025, at 11:00 AM, Dick Hardt <dick.hardt at hello.coop> wrote:
>>
>> I have no strong views on the scope name. Open to other ideas /
>> suggestions / opinions!
>>
>> Perhaps `cnf` to align with the claim?
>> ᐧ
>>
>> On Fri, Aug 29, 2025 at 3:57 PM <george at practicalidentity.com> wrote:
>>
>> Hi,
>>
>> Would it make sense to change the scope name identified in the
>> key-binding spec from something specific like ‘dpop’ to something more
>> generic? e.g. ‘id_token_kb’ ? Or maybe just make clearer that the RP is
>> looking for key bound tokens? e.g. ‘dpop_kb’? I just worry that ‘dpop’ by
>> itself does not communicate the intended behavior.
>>
>> Thoughts?
>>
>> George Fletcher
>> Identity Standards Architect
>> Practical Identity LLC
>>
>>
>>
>>
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