Consider this situation: Apache 2.2 is a reverse proxy with lots of configuration (multiple VirtualHosts, 4 backend servers, authentication based on Host and path) that I really like - because it works.
Now to speed up delivery of a Django site, I would like to cache all requests to a certain VirtualHost - except those that carry the Django session cookie (e.g. logged in staff requests). Now the request obviously Varys with cookies, e.g. a logged in user with cookie is always given a freshly rendered page while someone without cookies is given a cached response.
Vary: cookie would be the correct cache control header to do exactly that: Always freshly render when cookies present.
BUT then there is Google Analytics (GA) (and other cookie-based tracking mechanisms like eTracker) that always sets a cookie.
Can Apache ignore that GA-cookie and Vary on the Django session cookie??