I am having a little annoying situation here.
I have a server managed by plesk. In the /etc/apache2/apache2.conf mod_headers and mod_expires based configuration takes place. For example:
<filesMatch "\.(jpg|jpeg|png|gif|swf)$"> Header set Cache-Control "max-age=604800, public" </filesMatch>
This is working quite well.
I have a problem with some of my applications. I want to application to keep the control over cache if it wants to. Currently this is not possible, because header settings takes place emediatly before returning the response to the client, which means after the application has completeted all their actions. The headers set by the application will be overwritten.
Header merge Cache-Controll...
is not working though, because it just appends the given header string. And I doubt that browsers would handle headers like this one like I would like them to:
Cache-Control max-age=0, no-cache, no-store, must-revalidate, max-age=604800, public
My question now is: Is there a possibilty to set the header only if there is absolutly no content in the specific header "field"? I do not want my application to set any enviroment variables, because an application should not be changed to fit the needs of one server.
I also tried - for testing purpose only - to unset the header via vhost.conf for a specific domain. But it gets executed before the header setting in the apache2.conf, which means they would be overwritten, too.