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

Francis Pouatcha <> Sun, 26 July 2020 03:41 UTC

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From: Francis Pouatcha <>
Date: Sat, 25 Jul 2020 23:41:10 -0400
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To: Tom Jones <>
Cc: Justin Richer <>, Mike Jones <>, Fabien Imbault <>, Mike Varley <>, "" <>, Dick Hardt <>
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Subject: Re: [Txauth] Key handle vs client id & handle
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I just read through some work being done by Tom at the FIRE (Federated
Identifiers for Resilient Ecosystems) working group and it confirms my
intention of suggesting the consideration of a "Trust Framework" as a
context defining how to handle the client_id.

The procedure the GS applies to trust a client is derived from the "Trust
Framework" that governs the environment in which GS and Client are

In the European PSD2 ecosystem, National Country Authorities (a.k.a Market
Authorities or Regulators):
- delegate the production of client certificates to Trust Service Providers
(TSPs). TSPs are known certification authorities (CAs) in the corresponding
- maintain a register of Certified Third Party Providers (TPPs) at the
European Banking Association (EBA), where the validity of the TPP license
can be verified, in addition to the client certificate.

Designing an authorization framework around the PSD2 ecosystem, there is no
need to maintain any static or dynamic client_id. Each request is
associated with an SSL client certificate called QWAC (Qualified Website
Assertion Certificate).
- This certificate can be verified as the GS maintains a list of all known
TSP's CA authorized to release PSD2 client certificates.
- This certificate also contains the list of roles assigned to the TPP by
the regulator PSP_AS (bank), PSP_PI (payment initiation), PSP_AI (account
information), PSP_IC (card) sufficient for the client access control in the
PSD2 trust framework.
- This certificate contains a permanent "Competent Authority" that
uniquely identifies the NCA issuing the TPP license.
- This certificate contains a permanent "Authorization Number" that is
unique in the context of the NCA.
- so AuthorizationNumber@CompetentAuthority is globally unique in the
context of the PSD2 trust framework.

Given these facts, GS implementing PSD2 do not need to register clients.
- Each request of the client to the GS can be mTLS secured using the QWAC.
- GS can extract all information needed to perform authorization from that

This use case does not need an extra client_id at the protocol level.

This is:
- based on the experience we are making implementing PSD2,
- based on my reading Tom's FIRE use case in the health sector on the
sharing of Patient Health Information (PHI) among health care providers,

I suggest GNAP introduces the notion of "Trust framework" that governs the
environment in which RS, GS and Client interoperate. We can then delegate
the decision on specifying the necessity and functions of a client_id to
the trust framework.

On Thu, Jul 16, 2020 at 7:58 PM Tom Jones <>

> I have been working on different level s of identifier, but from the
> mobile app perspective. That's the hardest case as you need to boot strap
> trust. I suspect that in the web site case you will need these levels.
> Transport, application, real world.
> If anyone wants to work on these, let me know and I'll get you the links
> in Kantara.
> thx ..Tom (mobile)
> On Thu, Jul 16, 2020, 2:47 PM Justin Richer <> wrote:
>> For all of these, I still say we should have different levels of
>> identifier. A “client ID” should identify the client, and not be used as a
>> stand-in for other things.
>> Off the top of my head I think we might want to have identifiers,
>> assertions, proofs, and other trust-binding items for:
>>  - Organizations
>>  - Devices
>>  - Software applications
>>  - Software instances
>>  - Software versions
>> So if we’re going to talk about identifying these aspects, we should
>> tackle each as its own thing and not mush it all into “client_id”. That
>> way, hopefully, GNAP can have a much better idea what a “client” is than
>> OAuth 2 currently does.
>>  — Justin
>> On Jul 16, 2020, at 4:34 PM, Dick Hardt <> wrote:
>> One client identifier was a simplistic example. Org A may have numerous
>> clients, perhaps in different teams, perhaps in different services, each
>> with their own policy at Org B.
>> When one of the Org A clients makes a call to the Org B AS, it needs to
>> identify itself with some identifier so that Org B knows which policy to
>> enforce. Why not the Client ID?
>> I also agree with your comments that other client identification
>> situations are different, and forcing the same identification model on them
>> does not make sense, but I fail to see the value throwing out a concept
>> (client_id) that has worked well for the use cases it was designed for.
>> ᐧ
>> On Thu, Jul 16, 2020 at 1:08 PM Justin Richer <> wrote:
>>> I think that the cross-organizational trust model is an interesting one,
>>> and in fact it’s one of the things that’s pushed me away from a client_id.
>>> In the scenario that you describe, “client_id” is used to represent
>>> something that it was never meant to represent: the organization running
>>> the software, not the software itself. It isn’t a client_id, and while in
>>> OAuth 2 the client_id could be co-opted to carry that information, it’s
>>> considered bad practice to share client_ids between multiple pieces of
>>> software.
>>> I would argue that to address this use case properly, there should be
>>> another level of identifier to bridge that trust that the software can
>>> present, showing that it is a part of Organization A, and not Organization
>>> C. This isn’t a client identifier, it’s an organization identifier, and it
>>> should be separate. You might want to identify both the client instance as
>>> well as the organization it’s a part of, for example. This is part of the
>>> motivation behind putting “organizational data” within scope for the client
>>> to send to the AS, after all.
>>> Therefore, I strongly disagree that this scenario “requires” a client_id
>>> to be solved. In fact, I think that solving this scenario with a client_id
>>> is an anti-pattern that stems from OAuth 2’s over-reliance on client_id as
>>> a persistent identifier within the protocol, and we can and should do
>>> better with GNAP. It’s very similar to Mike Jones’s referenced federation
>>> document, where the client_id is co-opted as a means of bootstrapping
>>> client registration and discovery, or in the Solid Authentication
>>> specification which stuffs a WebID into the client_id field.
>>> With OAuth 2’s ecosystem, we’ve used the tools that we had to solve our
>>> problems, and come up with some very clever solutions. What I’m trying to
>>> argue to this community is that we are in a position to create our own,
>>> better tools.
>>>  — Justin
>>> On Jul 16, 2020, at 2:00 PM, Dick Hardt <> wrote:
>>> Justin,
>>> While I agree that the assumption in OAuth 2 that all Clients have a
>>> client_id is problematic, the requirement for a client_id in many use cases
>>> is still there, and it does not represent a piece of software, but a
>>> relationship between parties.
>>> Organization A writes client software that calls resources managed by
>>> the AS in Organization B. The client_id represents Organization A to
>>> Organization B. Organization B does not care what software Organization A
>>> is running, and there may be numerous pieces of software at Organization A
>>> that use the same client_id. The access granted by Organization B to
>>> Organization A needs to be able to be different than the rights granted to
>>> Organization C.
>>> I agree that we don't want to force all clients to have a client_id, and
>>> as discussed, there are a variety of inputs for an AS to accept calls from
>>> a piece of software, and often, that will be a particular *instance* of
>>> the software, but we also don't want to force clients to all be treated the
>>> same, because they are not..
>>> On Thu, Jul 16, 2020 at 8:24 AM Justin Richer <> wrote:
>>>> Exactly — when we start to look at it as managing the lifecycle of a
>>>> piece of software, instead of a registration at the AS, we can start
>>>> thinking in different terms what “trusting” the client means in the context
>>>> of what the client is doing. That trust could come from some kind of signed
>>>> attestation about the software (like the OAuth 2 DynReg software
>>>> statement), or it could come from some externally fetchable item (like a
>>>> Solid WebID, a DID, or the OIDC Federation extension), or it could come
>>>> from someone sitting at a console and typing in information and getting
>>>> back an identifier. And none of these need to pretend to be a global
>>>> “client id” for it to work. The world of clients is much more diverse than
>>>> OAuth 2 likes to admit, and we see that with trying to nail down a
>>>> “confidential” vs. “public” vs. “dynamic” vs. “static” vs. “automatic” vs.
>>>> “ephemeral” vs. … any number of other things.
>>>> OAuth 2 only needs client IDs because the front channel needs a way to
>>>> pass client identifiers when the client can’t authenticate itself directly.
>>>> We tried to get rid of this restriction with PAR and JAR together, but
>>>> there turned out to be corner cases in OAuth 2’s world that still needed
>>>> client_id, and implementations assumed it would be there anyway.
>>>> In GNAP, we can avoid that problem from the beginning by looking at the
>>>> model differently and understanding where we’re coming from, and why.
>>>>  — Justin
>>>> On Jul 16, 2020, at 3:49 AM, Fabien Imbault <>
>>>> wrote:
>>>> +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.
>>>> Fabien
>>>> 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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Francis Pouatcha
Co-Founder and Technical Lead
adorsys GmbH & Co. KG