public function extractHeaders()
    {
        $headers = [];
        $requestHeaders = array_keys($this->cors);
        foreach ($requestHeaders as $headerField) {
            $serverField = $this->headerizeToPhp($headerField);
            $headerData = isset($_SERVER[$serverField]) ? $_SERVER[$serverField] : null;
            if ($headerData !== null) {
                $headers[$headerField] = $headerData;
            }
        }
        return $headers;
    }