[Openid-specs-mobile-profile] auth_req_id and client_notification_token seem redundant

[Brian Campbell]

Eric raises a good question here that I don't have an immediate answer for.
Honestly, I hadn't really thought critically about the purpose of the
client_notification_token
relative to what the auth_req_id provides. Perhaps someone who was involved
when the client_notification_token concept was introduced can shed some
light on the motivations behind it and if there's reason for it beyond
what's mentioned here?

On Mon, Dec 31, 2018 at 6:07 AM Eric Fazendin via
Openid-specs-mobile-profile <openid-specs-mobile-profile at lists.openid.net>
wrote:

> auth_req_id and client_notification_token seem redundant.  Unless we can
> clarify why both are necessary, I suggest we remove
> client_notification_token from the spec.
>
>
> Based on 7.1, it's described as "It is a bearer token provided by the
> Client that will be used by the OpenID Provider to authenticate the
> callback request to the Client."
>
> 10.2 and 10.3.1 says, "The Client MUST verify the
> client_notification_token used to authenticate the request is valid and is
> associated with the auth_req_id received in the Ping callback."
>
> There is no further elaboration of why it's needed or what additional
> value it might provide the client.  Examples suggest it is in a GUID
> format.  Perhaps it could be a JWT and therefore reduce the state required
> to manage by the client, but it's not cryptographically bound to the
> auth_req_id, so the client is going to have to track the state of a given
> client_notification_token as being associated to a given auth_req_id.
>
>
> auth_req_id is described in 7.3 as "This is a unique identifier to
> identify the authentication request made by the Client."
>
> 7.4 says, "The Client MUST keep the auth_req_id in order to validate the
> callbacks received in Ping and Push modes or to use when making a token
> request in Poll and Ping modes."
>
>
> I don't understand the value of the client_notification_token when there
> is also the auth_req_id.  The client_notification_token adds unnecessary
> complexity to client implementations.  If the client wants to track
> authentication requests and associate them to Ping and Push Callbacks, they
> can do so with only the auth_req_id.
>
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