public static function getIp(): string
    {
        $ip = 'unknown';
        if ('' != ($ip = ($_SERVER['HTTP_X_FORWARDED_FOR'] ?? ''))) {
            if (false !== strpos($ip, ',')) {
                $ip = trim((string) end(explode(',', $ip)));
            }
        }
        // all ok
        elseif ('' != ($ip = ($_SERVER['HTTP_CLIENT_IP'] ?? ''))) {}
        elseif ('' != ($ip = ($_SERVER['HTTP_X_REAL_IP'] ?? ''))) {}
        elseif ('' != ($ip = ($_SERVER['REMOTE_ADDR_REAL'] ?? ''))) {}
        elseif ('' != ($ip = ($_SERVER['REMOTE_ADDR'] ?? ''))) {}

        return $ip;
    }