Active Directory IIS needs to get user logged in from client not @ server

Hi

I have an intranet site behind  a highly secure firewall.   I need to get the user at the client that is logged in

I am using this in c# in a web forms application

using System.DirectoryServices;
using System.DirectoryServices.AccountManagement;
using System.Security.Principal;
...
....
....
  String UserName = System.Security.Principal.WindowsIdentity.GetCurrent().Name;

It gives me the account of the server.  I need to get the username of the person logged in at the client.

How can I do this?  Any way to make it pass through from to IIS?  Maybe turn anonymous access off?

Thank You