Not that it answers the original question, but:
If you specify scope=openid, then the access_token can be used to call the /userinfo endpoint of the identity provider (Auth0), to get profile information about the user. If you specify an audience, then the access_token can be used to call the API specified in audience. You can specify both scope=openid and audience=xxx, and the access token will serve for the two purposes.
access_tokens with an audience are JWT (long format), whereas access_tokens issued without an audience are (currently) short opaque strings.