public function getRefreshToken($refresh_token)
    {
        $refreshToken = $this->em->getRepository('OAuth2ServerBundle:RefreshToken')->find($refresh_token);

        if (!$refreshToken) {
            return null;
        }

        // Get Client
        $client = $refreshToken->getClient();

        return array(
            'refresh_token' => $refreshToken->getToken(),
            'client_id' => $client->getClientId(),
            'user_id' => $refreshToken->getUserId(),
            'expires' => $refreshToken->getExpires()->getTimestamp(),
            'scope' => $refreshToken->getScope()
        );
    }