Expires directive does not allow to add immutable variable to Cache-Control header

[selivan@…]

expires directive sets 2 headers at once: Expires and Cache-Control.

Cache-Control is set to 'max-age=NNN', and can not be changed: using add_header just produces 2 Cache-Control headers.

I suggest to add optional flag [no_add_cache_control], that will stop expires directive from adding Cache-Control header and allow configuration like this:

expires no_add_cache_control 1d;
add_header Cache-Control "public, max-age=86400, immutable";

Cache-Control header has more variables than just max-age, it would be nice to be able to change it while still using Expires header for user agents that do not respect Cache-Control.

For example, immutable flag is useful to stop browsers like Firefox and Safari from creating requests for cached resources, just to get 304 response.

[Maxim Dounin]

Duplicate of #1188.