How to preprocess steps on Apache before sending a page to the User

Question

I have an Apache web server and I need to do some processes outside the web server when a user requests a certain page. I will try to be more clear: when a user requests page X, I have to start an external program, passing it some session parameters, wait for response, and then send the requested page to the user.

Is this possible to do this?

Answer 1

I used apache ext_mod_filter: http://httpd.apache.org/docs/2.0/mod/mod_ext_filter.html

Performances are not that great, but for my purposes it is ok.