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.