如何判断哪个帐户正在尝试访问ASP.NET Web服务？

I'm getting a 401 (access denied) calling a method on an internal web service. I'm calling it from an ASP.NET page on our company intranet. I've checked all the configuration and it should be using integrated security with an account that has access to that service, but I'm trying to figure out how to I'm getting a 401 (access denied) calling a met