Facebook Connect

We have a site that is currently not using Auth0 but a internal DB + Facebook Connect.
We are analyzing to see the impact of moving to Auth0. If we also migrate FB connect to Auth0 ( using Lock hosted form ) what are the impact.

  1. Does the callback to our site include the FB user ID so we can match that user to a existing profile
  2. Does all the users will have to re-approved the connection to Facebook since the login will not be initiated by Auth0 vs our current site. Can we avoid that by using the same Facebook App ID ?