Re: [Txauth] Key handle vs client id & handle

Fabien Imbault <> Thu, 16 July 2020 07:49 UTC

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From: Fabien Imbault <>
Date: Thu, 16 Jul 2020 09:49:31 +0200
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To: Justin Richer <>
Cc: Mike Varley <>, "" <>, Mike Jones <>, Dick Hardt <>
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Subject: Re: [Txauth] Key handle vs client id & handle
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+1 on that.

We can then see it more as life cycle management of the client than
registration per say, and this comes with many benefits compared to the
current client_id.


On Tue, Jul 14, 2020 at 9:32 PM Justin Richer <> wrote:

> I not only agree with Mike Jones that “automatic registration” should be
> part of the process, but I would argue that that kind of model should be a
> default mode of operation. If you have an identifier that you can send to
> short-circuit that, great! But we should focus on having the capability of
> inlining a lot of this information wherever possible. This is already the
> direction that the input proposals are heading.
> So I kind-of agree that “registration” is in scope for the protocol in
> general, and since both XYZ and Xauth have mechanisms that allow the client
> to present a key and get back an identifier that it can use in the future
> we have something equivalent.
> But I think there’s a little more to it than that: Ultimately, I think we
> should question thinking in terms of “registration”, a model which has
> hampered the OAuth 2 model in a lot of use cases. For example, the
> federation draft Mike Jones references below hacks the “client_id”
> parameter and makes it point to a document that the AS has to fetch. This
> construct is done for two reasons: (1) Oauth requires a “client_id” in the
> request and (2) it’s difficult to pass information by value to the AS due
> to front-channel restrictions. Since we’re defining a new protocol, we
> don’t need to hack that functionality into a “client ID” or equivalent and
> instead we can pass that information directly in the protocol. If we don’t
> assume that the client *has* to have a client ID equivalent, but it *can*
> have one in a set of defined circumstances, then I think we are in a much
> better spot. This is the reasoning for XYZ’s model of having clients
> identified by the key, and that key can potentially be passed by a
> reference identifier.
> I think all of the use cases that Mike Varley presents below are all valid
> directions, with the caveat that we shouldn’t assume a client should be
> presenting an ID at all steps. Mechanisms like software statements should
> be presentable apart from a client ID, as should on-device keys. We’re
> probably going to want extensions for device posture and other forms of
> attestation as well.
> This is one of the domains that I think we can clearly surpass OAuth 2’s
> flexibility and capabilities if we are willing to look past OAuth 2’s
> assumptions of what’s needed inline in the protocol.
>  — Justin
> On Jul 14, 2020, at 1:54 PM, Mike Varley <>
> wrote:
> Is client registration in scope for the protocol?
> A generic way of handling clients (via ID or Handle or Key or whatever) is
> to have processing rule on the AS such as “if the AS recognizes the client
> ID (and authentication of that client ID) then it may process the request
> on behalf of that client. If the AS does not recognize the client ID, it
> must treat this as a new client registration and evaluate any authorization
> evidence the client provides before enabling the client and mapping
> policies to that client” (this means dynamic or automatic clients need to
> provide additional assertions / software statements whatever to register
> their ID.
> Something like this allows for very flexible systems:
> System A can be unknown to the AS but can dynamically registered each time
> with an appropriate software statement
> System B can have a fairly stable client ID at the AS, but rotate that ID
> every month through automatic registration (with an assertion it got from
> the AS during a pre-registration for example)
> System C can pre-register with the AS for a client ID because it doesn’t
> deal with software statements etc…
> …
> And even ‘StatelessAS’ can operate by never storing client IDs because it
> will always just rely on the software statements.
> I think a client registration protocol that allows these scenarios would
> be very useful in GNAP, but hopefully avoiding having to define what
> ‘evidence’ the AS needs to accept for each scenario.
> Thanks,
> MV
> *From: *Txauth <> on behalf of Mike Jones <
> *Date: *Tuesday, July 14, 2020 at 12:18 PM
> *To: *Dick Hardt <>om>, "" <
>>gt;, Justin Richer <>
> *Subject: *Re: [Txauth] Key handle vs client id & handle
> I agree that there are significant differences between statically and
> dynamically registered clients and that’s appropriate to be able to
> syntactically differentiate between them at runtime.  For one thing, the
> resource requirements at the authorization server can be very different.
> We should also be thinking about how to include what the OpenID Connect
> Federation spec
> calls
> “Automatic Registration”.  This lets the client encode a registration
> request reference in the client ID, so no static or dynamic registration
> even occurs.  See
> <>
> .
>                                                        -- Mike
> *From:* Dick Hardt <>
> *Sent:* Friday, July 10, 2020 1:17 PM
> *To:*; Justin Richer <>du>; Mike Jones <
> *Subject:* Key handle vs client id & handle
> + Mike as he had interest in this topic
> My understanding is that an existing OAuth 2 client would use their
> current client id as their key handle, and a dynamic client (one that was
> not pre-registered) would be given a key handle by the AS.
> There are potentially some significant differences between a registered
> client, and a dynamic client to an AS.
> The AS is likely to know the identity of a registered client, and have
> different policies between the two types of clients. For example, a
> registered client may have access to a 'write" scope, while a dynamic
> client does not.
> The AS may have 100s or 1000s of registered clients, but a dynamic client
> may have 10Ms or 100Ms of instances, which may dictate separate storage
> services. Additionally, internal to the AS, which systems can write to the
> registered client store is going to be different than the dynamic
> client store.
> In XYZ, subsequent calls to the AS, both registered clients and dynamic
> clients pass a key handle, so there is no easy way to differentiate between
> the two.
> While the AS could embed semantics in the key handle identifier to
> indicate which identifiers are pre-registered vs dynamic, there are many
> cases where the AS does need to know the difference, so making the
> difference a feature of GNAP seems like a better path.
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