vinceve

    firewalls:
        main:
            pattern: ^/
            fos_twitter:
                  login_path: /user/login
                  check_path: /twitter/login_check
                  default_target_path: /
                  provider: fos_twitter_provider
            fos_facebook:
                  app_url: "http://apps.facebook.com/my-awesome-app"

vinceve

<?php

namespace My\UserBundle\Security\User\Provider;

use Symfony\Component\Security\Core\Exception\UsernameNotFoundException;
use Facebook;
use Symfony\Component\Security\Core\Exception\UnsupportedUserException;
use Symfony\Component\Security\Core\User\UserProviderInterface;
use Symfony\Component\Security\Core\User\UserInterface;
use \BaseFacebook;