protected function getDomain(array $config): string
    {
        $result = '';
        $parts = explode(',', $config['baseDn']);
        foreach ($parts as $part) {
            list($key, $value) = explode('=', $part);
            if ('dc' !== strtolower($key)) {
                continue;
            }

            $result .= '.' . $value;
        }

        $result = trim(trim($result, '.'));

        // fallback value
        if (empty($result)) {
            $result = $config['domain'] . '.com';
        }

        return $result;
    }