I'm a complete WCF novice. I'm trying to build a deploy a very, very simple IIS 7.0 hosted web service. For reasons outside of my control it must be WCF and not ASMX. It's a wrapper service for a pre-existing web application that simply does the following:

1) Receives a POST request with the request body XML-encapsulated form elements. Something like valuevalue. This is untyped XML and the XML is atomic (a form) and not a list of records/objects.

2) Add a couple of tags to the request XML and the invoke another HTTP-based service with a simple POST + bare XML -- this will actually be added by some internal SQL ops but that isn't the issue.

3) Receive the XML response from the 3rd party service and relay it as the response to the original calling client in Step 1.

The clients (step 1) will be some sort of web-based scripting but could be anything .aspx, python, php, etc.

I can't have SOAP and the usual WCF-based REST examples with their contracts and serialization have me confused. This seems like a very common and very simple problem conceptually. It would be easy to implement in code but IIS-hosted WCF is a requirement.

Any pointers?