/**
  * Grant a User Right
  * 
  * @param string $user_id
  * @param string $right
  * @return \argent_error|true
  */
 public static function grant_right($user_id, $right)
 {
     $error = new argent_error();
     $db = new argent_database();
     if (!self::object_exists($user_id)) {
         $error->add('1013', 'Invalid user account', $user_id, 'argent_uauth');
     }
     $right_id = self::right_exists($right);
     if (!$right_id) {
         $error->add('1042', 'Invalid user right', $right, 'argent_uauth');
     }
     if ($error->has_errors()) {
         return $error;
     }
     return argent_meta::relate($user_id, $right_id, 'user_right');
 }