Why do you need EnsLib.EDI.XML.Document?  If you already have persistent classes, then you can use the persistent classes in many places where EnsLib.EDI.XML.Document can be used.

Consider the flow of the access token:

1. Client requests the access token.

2. authorization server authenticates user and issues token

3. client receives token -- IsAuthorized will now return 1 in the same CSP session

4. client uses access token in Authorization header to authorize to resource server.

5. The resource server knows nothing about the access token at this point.  In order to validate the access token, the resource server either needs to check signatures (%SYS.OAuth2.Validation:ValidateJWT) or contact the authorization server (%SYS.OAuth2.AccessToken methods GetUserinfo or GetIntrospection).  Exactly which method to use depends on how the authorization server is configured. The standards do not specify in detail.  You need to contact the authorization server support folks.

There is not enough detail in the question for me to be able to comment.  I suggest that a call to support would be a good next step.