[OAUTH-WG] Re: AS Metadata client id parameter draft

[Karl McGuinness <[e-mail]>]

I strongly support standardizing an approach for a per-client metadata
mechanism to enable discovery of client-specific metadata values and reduce
change management risk as folks have indicated.  Okta shipped support for
client_id as query param for similar reasons almost 10 years ago!

I also think we need to consider the inverse for OAuth Client ID Metadata
Document (CIMD) where the authorization server identifier is an optional
parameter for the same reasons.

-Karl





On Mon, May 18, 2026 at 5:27 PM Max Gerber <max=[e-mail]>
wrote:

> It's a really interesting idea. Thanks Filip for the slides as well!
>
> > (1) do gradual rollouts of AS metadata changes client by client
>
> I 100% see the value in better-supporting gradual rollouts. Today, an AS
> can try *(emphasis on try!)* to feature flag responses based on IP
> address or User-Agent but both of those are *very* poor signals.
>
> > (2) customize metadata if necessary
>
> I am not a fan of long-lived customizations of metadata to support legacy
> clients, though I understand gradual rollouts and long-lived legacy flags
> are two sides of the same coin. I know it is not always possible or
> reasonable, but I would rather break old, insecure, and unmaintained
> clients than build tools to accommodate them.
>
> The security considerations could be worrisome; you call out that an
> attacker could enumerate which legacy features an AS still supports for a
> given client.
> This differs from observing that client's behavior—a client might remove
> the use of the `implicit` grant from their flow, but still be permitted by
> the AS to use it for legacy reasons. Using this endpoint, an attacker could
> determine that fact and attempt to exploit it.
>
>
> On Mon, May 18, 2026 at 10:08 AM Andy Barlow <[e-mail]>
> wrote:
>
>> I fully support any and all effort on this topic.
>>
>> On Mon, 18 May 2026 at 17:58, Filip Skokan <[e-mail]> wrote:
>>
>>> Hello Nick,
>>>
>>> Let me know what you all think.
>>>
>>>
>>> Back at IETF 121 I presented this related/similar idea:
>>>
>>>    - https://youtu.be/_kNpecjcj64?t=6354
>>>    -
>>>    https://datatracker.ietf.org/meeting/121/materials/slides-121-oauth-sessa-client-id-hint-for-authorization-server-metadata-requests-00
>>>
>>> I haven't had a chance to follow up on it since
>>>
>>> S pozdravem,
>>> *Filip Skokan*
>>>
>>>
>>> On Mon, 18 May 2026 at 17:09, Nick Watson <nwatson=
>>> [e-mail]> wrote:
>>>
>>>>
>>>> https://njwatson32.github.io/as-metadata-client-id/draft-watson-oauth-as-metadata-client-id.html
>>>>
>>>> I've written up a quick draft on supporting a client_id parameter on AS
>>>> Metadata, which would allow the AS to (1) do gradual rollouts of AS
>>>> metadata changes client by client and (2) customize metadata if necessary
>>>> (e.g. for clients participating in beta programs of upcoming drafts).
>>>>
>>>> AS can also choose to ignore the client_id parameter completely and
>>>> continue serving a statically cached global AS metadata file.
>>>>
>>>> I had this idea recently when implementing support for 9207 (iss
>>>> parameter) and running into poorly behaved clients handling these updates
>>>> badly. The draft I'm proposing would have allowed me to avoid making global
>>>> changes to AS metadata, and even do a synchronized rollout of returning
>>>> `iss` from the authorization endpoint and
>>>> declaring authorization_response_iss_parameter_supported.
>>>>
>>>> Let me know what you all think.
>>>>
>>>> Nick
>>>>
>>>> PS: I've also proposed the "reverse" of this for CIMD in this issue
>>>> <https://github.com/oauth-wg/draft-ietf-oauth-client-id-metadata-document/issues/78>
>>>> .
>>>>
>>>> --
>>>> Nick Watson | Software Engineer | [e-mail] | [phone]
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