I have enabled in my Web.config the GZIP compression, and I'm glad that it automatically adds the HTTP header "Vary: Accept-Encoding".
The problem is that IIS is overwriting the "Vary:*" that ASP.NET returns by default.
The issue is that in POST calls, the "Vary" header has to be "*", because it means the response depends on things that are not in the URL or the HTTP headers... as far as I know. A POST call with a "Vary:Accept-Encoding" could be wrongly cached, am I right?
What I want to do is tell IIS to respect the previous "Vary" header if any.