How do I fetch the domainusername from a WCF service call made from MVC application?

I have an ASP.NET service hosted on IIS running the App pool with a service account. I need to fetch the username and domain of the user calling the service from an MVC controller. How can I fetch the required details?
The details need to fetched in service and not sent from MVC application.
I have tried using WindowsIdentity.GetCurrent().Name but it gives me the service account details.

ASP.NET Fire and Forget (One Way) Web Service

I’ve create a regular old ASMX web service in ASP.NET and added SoapDocumentMethod(OneWay = true)] to the function call as I’ve read this is supposed to make the call Asynchronous. However I call this in my code and it definitely does not make the call asynchronous, my page just sits there waiting for the function to finish working. What gives?