This is a follow up of r1808746 after a chat with Yann on dev@:
- the HTTP:Host variable suffers from the same problem - the strcasecmp should be used to allow case-sensitive comparisons. - in mod_rewrite is less cumbersome and more clean to just make the Host header check in lookup_header, so it will be automatically picked up by every part of the code that uses it. It shouldn't be a relevant overhead for mod_rewrite.
"The "Vary" header field in a response describes " "what parts of a request message, " "aside from the method, Host header field, [...]"
I had a chat with the folks in #traffic-server and they don't see much point in having a Vary: Host header, plus it was reported that Varnish doesn't like it very much (namely it does not cache the response when it sees the header, links of the report in the PR).
I don't see much value in this behavior of httpd so I am inclined to remove this response header value, but I'd be glad to get a more experienced opinion.