static function refresh_session_if_staying_logged_in()
 {
     if (!isset($_SESSION['id']) && isset($_COOKIE['stay_logged_in_hash']) && isset($_COOKIE['stay_logged_in_id'])) {
         // no session running but user has cookies indicating that he stayed logged in
         // confirm if the user stayed logged in
         if (Database::check_stay_logged_in($_COOKIE['stay_logged_in_id'], $_COOKIE['stay_logged_in_hash'])) {
             // the user stayed logged in
             // set the session cookie with the users id
             $_SESSION['id'] = $_COOKIE['stay_logged_in_id'];
         }
     }
 }