An admin can enable users to authenticate with their Facebook account

This test requires a Facebook client ID and secret and account for use in testing.

1. Log in as an admin and set up and configure the OAuth 2 Facebook service with a client ID and secret, as described in the documentation OAuth2 Services and OAuth 2 Facebook service.
2. Enable the OAuth 2 authentication plugin.
3. Log out then try to log in with a Facebook account using the "Log in using your account on Facebook" button on the login page.
4. Check that you see a message saying that a confirmation email has been sent.
5. Check you email and follow the link in the confirmation email.
6. Check that a new account is created with name as on Facebook.
7. Log out and log in again as admin and go to Manage authentication.
8. Check that for OAuth 2 the number of users has increased by one.