Changing upstream response headers, before nginx caching decisions

[Gryzli Bugbear]

Hello everybody,


I have the following working scheme:

Client --> Nginx [caching] --> Apache [backend]


Sometime the backend returns headers, which I want to modify before 
nginx caching engine decides how to treat them. One such example is when 
backend returns Vary:  header.


I want to achieve the following:


[Apache backend returns Vary: User-Agent, Header2] --> [Nginx Modifies 
"Vary:" and removes User-Agent] --> [Nginx caching sees only 'Vary: 
Header2' (without User-Agent)] --> The final result is that Nginx cache 
wont take 'User-Agent' into vary considerations. (no cache object per UA).

That's just an example. I would like to do such modification with other 
headers also (for example Cache-Control).

Currently I'm already using Nginx Lua integration, but there is no hook 
point before the caching engine.


Would be happy for any suggestions about achieving this scenario.


Regards