Barryvdh\Cors\Stack\CorsService::checkPreflightRequestConditions PHP Method

    private function checkPreflightRequestConditions(Request $request)
    {
        if (!$this->checkOrigin($request)) {
            return $this->createBadRequestResponse(403, 'Origin not allowed');
        }
        if (!$this->checkMethod($request)) {
            return $this->createBadRequestResponse(405, 'Method not allowed');
        }
        $requestHeaders = array();
        // if allowedHeaders has been set to true ('*' allow all flag) just skip this check
        if ($this->options['allowedHeaders'] !== true && $request->headers->has('Access-Control-Request-Headers')) {
            $headers = strtolower($request->headers->get('Access-Control-Request-Headers'));
            $requestHeaders = explode(',', $headers);
            foreach ($requestHeaders as $header) {
                if (!in_array(trim($header), $this->options['allowedHeaders'])) {
                    return $this->createBadRequestResponse(403, 'Header not allowed');
                }
            }
        }
        return true;
    }