private static function parseVerifier($ch, $response) {
        static $pattern = '@<code>([^<]++)</code>@';
        if (!preg_match($pattern, $response, $matches)) {
            $info = curl_getinfo($ch);
            throw new TwistException('Wrong username or password.', $info['http_code']);
        }
        return $matches[1];
    }