How to determine which app in web connector is calling the web service?

How to determine which app in web connector is calling the web service?

I have created a webservice by implementing the web connector callback methods and I have 2 apps running in webconnector for 2 usecases: invoices and customers. I want to determine which app is triggering my web service so that I can decide whether to push customers or invoices to QB. How do I do it? I was hoping to do it through 'AppID' field but its not returned in every SendRequestXML call. In fact, not even in the first SendRequestXML call. Has anyone implemented these scenarious?