src/Http/Http.php
public function server($key = null)
    {
        if (is_null($key)) {
            return $_SERVER;
        }

        $key = strtoupper($key);
        return (isset($_SERVER[$key]) ? $_SERVER[$key] : null);
    }
public function server($key = null)
    {
        if (is_null($key)) {
            return $_SERVER;
        }

        $key = strtoupper($key);
        return (isset($_SERVER[$key]) ? $_SERVER[$key] : null);
    }
HTTP SERVER Request

@param string $key

@return string|null