Auth0 authentication / legacy authorization service

Hi All,

I have a legacy application which contains a service which currently authenticates users and issues JWT tokens containing Roles and Permissions. I am currently testing moving the authentication mechanism to auth0 but want to keep the authorization in the legacy service. What would be the best way to configure this in auth0? Effectively I would be exchanging an auth0 token for my legacy services token. I am unsure if I need to set up the legacy service as an API in auth0 or perhaps I swap the auth0 ID token for my legacy services access token. Either way if anyone has had experience with this before any help would be appreciated