Querying for roles within a user group


I am fairly new to using Auth0 for my authentication. What I am trying to do is allowing a user to select a group (querying possible groups from the auth0 authorization extension API). and select certain users within that group that have a specific role. Getting the users for a group is not hard, but the user info of these users does not contain their role, even though I have assigned them to one. I could query for the role in each individual user but that would just be horribly inefficient.

I have tried using the authorization extension. This should include roles in the app_metadata… but I cannot assign the roles for the correct application because roles can only be assigned to applications that are not defined as API… (Note: I am using the role system within the authorization extension. I also use groups with this extension and they do show up…)

Can anyone point me in the right direction?