intercept soap requests and http requests using php

Question

I am trying to build an intrusion detection application and wanted to intercept the http or soap requests at the server before they are processed. I want to scan them and then deliver them to the server for processing. Can anyone help in how I can write such a script to intercept the requests using php ? I saw that creating a proxy and channeling all requests through that might help. Is this the best way ? If so, how do I develop a proxy script ?