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

Justin Richer <> Tue, 14 July 2020 19:31 UTC

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From: Justin Richer <>
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Date: Tue, 14 Jul 2020 15:31:31 -0400
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To: Mike Varley <>
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Subject: Re: [Txauth] Key handle vs client id & handle
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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 < <>>, " <>" < <>>, 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 < <>>; 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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