class AppKernel extends Kernel
    public function registerBundles()
        {
            $bundles = array(
                ...
                new AdrienBrault\OAuth2FacebookGrantBundle\ABOAuth2FacebookGrantBundle(),

ab_oauth2_facebook_grant:
    user_provider: bundle.facebook_user_provider
    uri: "http://grants.yourapi.com/facebook_access_token"

<?php

namespace AdrienBrault\Core\UserBundle\Security;

use Symfony\Component\Security\Core\User\UserProviderInterface;
use Symfony\Component\Security\Core\User\UserInterface;

use FSC\Core\UserBundle\Manager\UserManager;

class FacebookUserProvider implements UserProviderInterface
{
    protected $userManager;

    public function __construct(UserManager $userManager)
    {
        $this->userManager = $userManager;
    }

    public function loadUserByUsername($facebookId)
    {
        $userRepository = $this->userManager->getRepository();

        return $userRepository->findOneBy(array(
            'facebookID' => $facebookId,
        ));
    }

    public function refreshUser(UserInterface $user)
    {
        $class = get_class($user);
        if (!$this->supportsClass($class)) {
            throw new UnsupportedUserException(sprintf('Instances of "%s" are not supported.', $class));
        }

        return $this->loadUserByUsername($user->getFacebookID());
    }

    public function supportsClass($class)
    {
        return $this->userManager->supportsClass($class);
    }
}