This question is a little stale, but I might be able to shed some light on the null access token.
I have been having very similar issues, but I did find that I needed to set the right configuration options in the laravel-auth0.php file in order to access the token later:
'persist_user' => true,
'persist_access_token' => true,
'persist_id_token' => true,
The second option is the one that persists the token to the user information. You can get at it with Auth0::getAccessToken() or from the user with Auth::user()->getAuthPassword().