Any Advice on cXML?

I have a customer who will be accessing our site through Coupa, a 3rd party that uses the cXML standard. The cXML itself is not that hard, just xml with specific tag layout/data and verified by dtd file at The hardest part is finding php examples to follow, the cXML manual is 500 pages long with not a mention of php, just asp.

What I know is that Coupa will send via post a setup request cXML to an action defined in my controller. When my controller action receives this post, it is to send back a response. Whether the received post is a string or a file, I do not know, I could not get a straight answer on that. This makes me wonder which one I have to send back as a response. If I find out, I will update.

Until I find out more from Coupa, I would like to do some testing on localhost. I am wondering how to set it up. I am okay with my Yii site end of it with the relevant controller, I am not sure what to do to simulate the 3rd party site sending the xml to start the process. My research so far leads me to believe that curl might be the way to do this but I have never used it before.

After some more research I have discovered some methods that check the incoming cxml and write the proper response. The idea of simulating the 3rd party site was not necessary. When I am closer to completion and after some live testing from the actual 3rd party site, I will post some code that might be helpful.