Is this proxying possible

I have a little problem that I though I could solve in a simple way using
apache, but after going through the documentation I am not so sure...

Basically the problem is that on my server I get some POST messages that I
would like to do the following with:
a: log the entire message to the file system
b. add a field to the message itself (ideally within the http body)
c. proxy the message to another server/ port for processing

My first idea was that this could be done with a few rewrite rules and a
perl script, but I'm beginning to get som doubts. Is there anyone out there
that could help me...please...?