Code change:
12.34. <ins> GNAP allows the RO to be contacted by the AS asynchronously, outside the regular flow of the protocol.  This allows for some advanced use cases, such as cross-user authentication or information release, but such advanced use cases have some distinct issues that implementors need to be fully aware of before using these features. First, in many applications, the return of a subject information to the client instance could indicate to the client instance that the end-user is the party represented by that information, functionally allowing the end-user to authenticate to the client application. While the details of a fully functional authentication protocol are outside the scope of GNAP, it is a common exercise for a client instance to be requesting information about the end user.  This is facilitated by the several interaction-start defined in GNAP that allow the end user to begin interaction directly with the AS. However, when the subject of the information is intentionally not the end-user, the client application will need some way to differentiate between requests for authentication of the end user and requests for information about a different user.  Confusing these states could lead to an attacker having their account associated with a privileged user.  Client instances can mitigate this by having distinct code paths for primary end user authentication and requesting subject information about secondary users, such as in a call center.  In such use cases, the client software used by the resource owner (the caller) and the end-user (the agent) are generally distinct, allowing the AS to differentiate between the agent's corporate device making the request and the caller's personal device approving the request. Second, RO's interacting asynchronously do not usually have the same context as an end user in an application attempting to perform the task needing authorization.  As such, the asynchronous requests for authorization coming to the RO from the AS might have very little to do with what the RO is doing at the time.  This situation can consequently lead to authorization fatigue on the part of the RO, where any incoming authorization request is quickly approved and dispatched without the RO making a proper verification of the request.  An attacker can exploit this fatigue and get the RO to authorize the attacker's system for access.  To mitigate this, AS systems deploying asynchronous authorization should only prompt the RO when the RO is expecting such a request, and significant user experience engineering efforts need to be employed to ensure the RO can clearly make the appropriate security decision.  Furthermore, audit capability, and the ability to undo access decisions that may be ongoing, is particularly important in the asynchronous case. </ins> An attacker may aim to gain access to confidential or sensitive resources.  The measures for hardening and monitoring resource server systems (beyond protection with access tokens) is out of the scope of

Related discussion:
text: Adds the field for requesting information for a specific user, separate from identifying the current end-user. Also adds a security considerations section addressing asynchronous authorization methods.
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Normally we think about releasing subject information being about the current end-user, but that's not necessarily universal. The use case from CIBA: Alice is a support engineer with a company Bob is a customer of that company Bob calls the company and talks to Alice Alice needs to authenticate, from her system, that Bob is the person tied to the account in question Alice's client messages the AS to request Bob's information (probably including an identifier for Bob in the request) The AS reaches out to Bob to approve Alice's client to get Bob's information Bob approves Alice's request (probably on a pre-enrolled device) The AS sends Bob's information back to Alice's client Note a few key assumptions with this: At no point does Alice's client think that Bob is logging in. Alice and Bob both need accounts of some type at the AS Alice's account (or client) need the rights to request someone else's info Bob's approval mechanism needs to be tied to his account ahead of time (since Bob isn't running the client and the AS needs to reach out to him out of band) Bob's approval needs to be clearly directed to tell Bob that it's Alice (and alice's client) asking for his info Alice might need to log in / interact with the AS as part of this, or it might be tied to the client instance (maybe Alice has logged in for the day and that association is remembered by the AS?)
This is an interesting use case. Yet CIBA doesn't necessarily require an AS to work, as long as one is only interested in getting scopes. Is there a generic use case for cross-user subject information + required AS? Or maybe we should explain the added value of the AS in that specific case ?
We will add an example in section D that shows how this would work and verify that the language around subject identifiers is sufficiently robust to encapsulate this. This might also add additional security and privacy considerations when used in this mode because multiple people are now involved explicitly.
I think this could be marked as NEEDS TEXT ?
I think it mostly just needs to be added as an example, and I can do that.