public function random_string($length = 32)
    {
        return substr(str_shuffle(str_repeat(
            $x = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ',
            ceil($length / strlen($x))
        )), 1, $length);
    }