core-bundle/src/EventListener/MergeHttpHeadersListener.php
public function onKernelResponse(FilterResponseEvent $event): void
    {
        if (!$this->framework->isInitialized()) {
            return;
        }

        // Fetch remaining headers and add them to the response
        $this->fetchHttpHeaders();
        $this->setResponseHeaders($event->getResponse());
    }
public function onKernelResponse(FilterResponseEvent $event): void
    {
        if (!$this->framework->isInitialized()) {
            return;
        }

        // Fetch remaining headers and add them to the response
        $this->fetchHttpHeaders();
        $this->setResponseHeaders($event->getResponse());
    }
Adds the Contao headers to the Symfony response.