code: 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;
      }
docs: Extract CORS headers from the request
  @return array CORS headers to handle