Here is the list of links about apache module development that I found useful:
Apache Modules Development and Debugging
libapr(apache portable runtime) programming tutorial
The Apache Modules Book: Application Development with Apache
Mailing list archives
Apache at WebÞing
Writing portable C code with APR
Apache Modeling Project
You can also download the apache source code and experiment with mod_example.
I'd agree with Aiden. Writing Apache modules is not for the faint hearted and you definitely don't want to go there unless you absolutely must. You would need to be prepared to become very conversant with how Apache works.
If you still think you need to, then look at:
This is a library which uses existing Apache Runtime Libraries and which provides higher level functionality for dealing with POST data, cookies etc from C code hooked into Apache via a custom module.
The book Aiden mentions though is a bit dated. Better off getting:
I did create a mod_cpp once. It basically was written in c, but loaded a .so which was in turn written in C++.
Its performance was really good, but lacked a lot of things that we take for granted in things like PHP (sessions, HTML un/escaping, etc). It did use a template engine to separate the HTML from the C++.
I tell you, the initial set-up was a lot of work (the mod_cpp part); after that, it was kinda easy to write the .so's. I even tried to create an sf.net project to open-source it, but I never got around to actually porting it :-(
In summary: I did not find anything like that on the net, did it myself and found out to be a lot more work then I anticipated, but the result was very cool! This helped me a lot: Apache Modules