Re: [GNAP] DID as sub_id or assertion?

[Justin Richer <[e-mail]>]

Fabien,

Exactly, this is why I am more and more thinking that the core protocol should focus on the client instance->AS / client instance->RS connections (for which the token is opaque) and a secondary document would talk about the AS<->RS connection (for which the token is not opaque).

The mapping of the AS and RS roles is also key. In OAuth 1, these were a single entity known as the “server”. In OAuth 2, we decided to split the roles to ease the discussion of how to deploy them. OAuth 2 doesn’t say anything about how they relate to each other except that the RS trusts tokens coming from the AS. An AS could have multiple RS’s that it protects, an RS could accept tokens from multiple AS’s, these relationships could be statically configured, they could be dynamic at runtime, etc. The community has come up with two key extensions — JWTs and Introspection — that allow for interoperable ways to make this connection, but OAuth 2’s core doesn’t actually care how this happens and it could be proprietary or internal (and often times is in practice). But in all cases, the RS has outsourced its trust to the AS to create tokens the RS will accept. 

 — Justin

> On Mar 18, 2021, at 1:13 PM, Fabien Imbault <[e-mail]> wrote:
> 
> Hi Justin, 
> 
> "The access token is fundamentally a conversational artifact between the AS and the RS which the client is the carrier of."
> That's right, and a good opportunity to distinguish between the need for token inspection (i.e. a runtime verification, wherever that may be) and the need to negotiate the token format (a discovery). That last part could very well be an extension, as a way to open up the ecosystem beyond JWTs (which are fine, but come with their own limitations). 
> 
> Fabien
> 
> On Thu, Mar 18, 2021 at 5:59 PM Justin Richer <[e-mail] <mailto:[e-mail]>> wrote:
> On Mar 18, 2021, at 11:30 AM, Alan Karp <[e-mail] <mailto:[e-mail]>> wrote:
>> 
>> Justin Richer <[e-mail] <mailto:[e-mail]>> wrote:
>> On Mar 18, 2021, at 12:08 AM, Alan Karp <[e-mail] <mailto:[e-mail]>> wrote:
>>> 
>>> Adrian Gropper <[e-mail] <mailto:[e-mail]>> wrote:
>>> 
>>> Is there an AS involved in the delegation? How and where in the lifecycle of the protected resource? 
>>> 
>>> If tokens are certificates, the AS need not be involved in subsequent delegations.  The AS must be involved if the tokens are opaque. 
>> 
>> Tokens are opaque to the client instance. They are not opaque to the AS. They might be opaque to the RS, but that depends on the kind of relationship the RS and AS have. GNAP should allow different options here as there are different use cases for that.
>> 
>> Tokens are not opaque to the client in SPKI, zcap-ld, Orie's implementation with VCs, or our Zebra Copy work.  Why must they be in GNAP?
> 
> The existence of the AS is exactly the reason for this. The AS is the role that “knowledge about the token contents” has been outsourced to in the GNAP model (which is based on the OAuth model).
> 
> It brings significant simplicity for the client developer. The question I have is — why does the client need to know what’s in the token? Not if they could possibly know, but why would we expect a client to know and manage the contents of the token? 
> 
> The access token is fundamentally a conversational artifact between the AS and the RS which the client is the carrier of. The client is not the audience of the token, nor the creator of the token, nor even the manager of the token and the rights it represents. The client as a simple carrier is a powerful model that allows the security layer to get out of the way of the actual application logic that developers want to do.
> 
>  — Justin
> 
>> 
>> --------------
>> Alan Karp
>> 
>> 
>> On Thu, Mar 18, 2021 at 4:56 AM Justin Richer <[e-mail] <mailto:[e-mail]>> wrote:
>> On Mar 18, 2021, at 12:08 AM, Alan Karp <[e-mail] <mailto:[e-mail]>> wrote:
>>> 
>>> Adrian Gropper <[e-mail] <mailto:[e-mail]>> wrote:
>>> 
>>> Is there an AS involved in the delegation? How and where in the lifecycle of the protected resource? 
>>> 
>>> If tokens are certificates, the AS need not be involved in subsequent delegations.  The AS must be involved if the tokens are opaque. 
>> 
>> Tokens are opaque to the client instance. They are not opaque to the AS. They might be opaque to the RS, but that depends on the kind of relationship the RS and AS have. GNAP should allow different options here as there are different use cases for that.
>> 
>> It would probably be worthwhile to separate the portions of the spec that talk about the RS-AS relationship into its own standalone document. A similar approach was taken in UMA2 and it was helpful. (Though admittedly, as with anything, there are missteps there that we can hopefully learn from.)
>> 
>>  — Justin
>> 
>>> 
>>> --------------
>>> Alan Karp
>>> 
>>> 
>>> On Wed, Mar 17, 2021 at 8:54 PM Adrian Gropper <[e-mail] <mailto:[e-mail]>> wrote:
>>> Sure! 
>>> 
>>> Is there an AS involved in the delegation? How and where in the lifecycle of the protected resource? 
>>> 
>>> Also your use of "the client" seems to imply that either there is only one client or the client doesn't matter. Which is it?
>>> 
>>> Adrian
>>> 
>>> On Wed, Mar 17, 2021 at 11:43 PM Fabien Imbault <[e-mail] <mailto:[e-mail]>> wrote:
>>> Thanks for that. 
>>> 
>>> Trying to reframe it:
>>> GNAP is defined as a delegation protocol so the main intent is related to a delegate of the RO (i.e. the end user) that wishes to access the RO's protected resources, through the client. 
>>> 
>>> Fabien 
>>> 
>>> Le jeu. 18 mars 2021 à 04:29, Adrian Gropper <[e-mail] <mailto:[e-mail]>> a écrit :
>>> At various points in the lifecycle of the protected resource the client at the resource server (RS) might be:
>>> The RO (subject) user agent trading payment for a service promise
>>> The RO user agent using the promise to access the protected resource
>>> A delegate of the RO user agent using a different client
>>> What's vague is where the GNAP AS enters the picture as described above. How would you describe it?
>>> 
>>> Adrian
>>> 
>>> 
>>> On Wed, Mar 17, 2021 at 10:20 PM Fabien Imbault <[e-mail] <mailto:[e-mail]>> wrote:
>>> Hi Adrian
>>> 
>>> I'm still confused why you're saying the terminology is vague. 
>>> I get the "power" neutrality is not to your liking, but RQ / user agent is no better in my view. 
>>> 
>>> Can you elaborate? 
>>> 
>>> Fabien 
>>> 
>>> Le jeu. 18 mars 2021 à 00:18, Adrian Gropper <[e-mail] <mailto:[e-mail]>> a écrit :
>>> I'm sure you're right. Our vague terminology around client and end-user leads to my confusion. If GNAP is primarily about delegation then, of course, we should avoid any incentives to impersonate or we're wasting our time. This is partly why I'm trying to study up on capabilities and asking for expert advice from folks like Alan Karp and Mark Miller (cc'd)
>>> 
>>> As best I can understand it, the RS has only two choices, it can:
>>> store an attribute of the RO a [DID, email address, GNAP AS URL], or
>>> hand the RO a capability as a sort-of promise and avoid making any entries in an ACL or equivalent.
>>> When a token comes back to the RS, it will either be:
>>> validated according to something associated with the stored RO attribute, or
>>> signed by the RS itself.
>>> Either way, trust in the client seems moot.
>>> 
>>> Adrian
>>> 
>>> 
>>> 
>>> On Wed, Mar 17, 2021 at 5:29 PM Justin Richer <[e-mail] <mailto:[e-mail]>> wrote:
>>> On Mar 17, 2021, at 4:55 PM, Adrian Gropper <[e-mail] <mailto:[e-mail]>> wrote:
>>>> 
>>>> On Wed, Mar 17, 2021 at 4:23 PM Tobias Looker <[e-mail] <mailto:[e-mail]>> wrote:
>>>> <snip>
>>>> > A client might not have a DID but it could have a VC as a certificate of authenticity linked to some audit mechanism.
>>>> 
>>>> To me a VC would come under the assertions umbrella (that is to say a VC could be one type of valid assertion). The client may possess or been presented with a VC that it could include in its request to the AS as a way to identify the subject and perhaps prove authentication and authorization.
>>>> 
>>>> I do not assume that the client that interacts with the AS to make a request and receive a token is the same as the client that will present the token to the RS. In the US HIPAA use-case, for example, the root of trust is a contract between the patient-subject and the doctor-requesting party but the doctor workflow is expected to delegate the token to some other end-user that may be using a totally different client such as an EHR.
>>>> 
>>> 
>>> If the client that gets the token is not same as the client that uses the token, that is a violation of core security principles as it allows for (and really designs for) impersonation by client software. I would have no reason to trust client software that would hand its credentials over to another piece of software, and in fact I shouldn’t trust it. 
>>> 
>>> I think you may be conflating several different kinds of parties under the “client” umbrella here, though. It’s entirely possible that one client might call an RS that in turn acts as a client for something else down stream. But each of those hops is different from the last.
>>> 
>>>  — Justin
>>> 
>> 
>