We wanted to use a mix of auth0 and personal datastore. So we needed a way to connect both of them.
Our current solution handles authorization and authentication with auth0 and stores user relevant data (such as avatar) in our own datastore.
The challenge was to identify users which are not available in our datastore and connect them to an auth0 user and the other way round. We opted for a simple check of the username to get a first version running.