How to add additional cache-states for HttpCache in Shopware 6?

I need to distinguish further regarding cache-states for the http-cache. There are two additional parameters, that I want to take into account when caching the response with the HttpCache:

• The value of the Cloudflare header "cf-ipcountry" in the request
• the value of an additional cookie that can be set during the request, lets call it "example-cookie"

How can this be achieved?

I think I found the answer: there is \Shopware\Storefront\Framework\Cache\Event\HttpCacheGenerateKeyEvent which is dispatched during the build of the cache-hash (which is used to look up if there is already a cached response or not).

By creating a subscriber to this event you can modify the cache hash taking your own parameters into regard. So for my example, it would look like something like this:

class CacheKeySubscriber implements EventSubscriberInterface
{

    public static function getSubscribedEvents(): array
    {
        return [
            HttpCacheGenerateKeyEvent::class => 'onGenerateCacheKey',
        ];
    }

    public function onGenerateCacheKey(HttpCacheGenerateKeyEvent $event): void
    {
        $request = $event->getRequest();
        $originalHash = $event->getHash();

        $countryHeaderValue = $request->headers->get('cf-ipcountry');
        $exampleCookieValue = $request->cookies->get('example-cookie');

        $dataToHash = '';
        if ($countryHeaderValue) {
            $dataToHash .= '-country:' . $countryHeaderValue;
        }
        if ($exampleCookieValue) {
            $dataToHash .= '-exampleCookieValue:' . $exampleCookieValue;
        }

        $newHash = hash('sha256', $originalHash . $dataToHash);
        $event->setHash($newHash);
    }
}