Get Windows logged-in Username ASP .net

I have an application deployed on IIS 8 having forms authentication mode. Now there is a requirement where business wants to show a popup message and create an audit log if the Windows User and the Application user is different.

For this I want to get the Windows Logged in user on logincontrol of the applicaiton. I have tried many ways but nothing is helping.

Please guide me if it is possible or not.

Guys anyone.. Please help me...

I use this site as a reference:

http://richhewlett.com/2011/02/15/getting-a-users-username-in-asp-net/

(reposted summary in case site goes down)

Scenario 1: Anonymous Authentication in IIS with impersonation off.

HttpContext.Current.Request.LogonUserIdentity.Name  COMPUTER1\IUSR_COMPUTER1
HttpContext.Current.Request.IsAuthenticated False
HttpContext.Current.User.Identity.Name  -
System.Environment.UserName ASPNET
Security.Principal.WindowsIdentity.GetCurrent().Name    COMPUTER1\ASPNET

Scenario 2: Windows Authentication in IIS, impersonation off.

HttpContext.Current.Request.LogonUserIdentity.Name  MYDOMAIN\USER1
HttpContext.Current.Request.IsAuthenticated True
HttpContext.Current.User.Identity.Name  MYDOMAIN\USER1
System.Environment.UserName ASPNET
Security.Principal.WindowsIdentity.GetCurrent().Name    COMPUTER1\ASPNET

Scenario 3: Anonymous Authentication in IIS, impersonation on

HttpContext.Current.Request.LogonUserIdentity.Name  COMPUTER1\IUSR_COMPUTER1
HttpContext.Current.Request.IsAuthenticated False
HttpContext.Current.User.Identity.Name  -
System.Environment.UserName IUSR_COMPUTER1
Security.Principal.WindowsIdentity.GetCurrent().Name    COMPUTER1\IUSR_COMPUTER1

Scenario 4: Windows Authentication in IIS, impersonation on

HttpContext.Current.Request.LogonUserIdentity.Name  MYDOMAIN\USER1
HttpContext.Current.Request.IsAuthenticated True
HttpContext.Current.User.Identity.Name  MYDOMAIN\USER1
System.Environment.UserName USER1
Security.Principal.WindowsIdentity.GetCurrent().Name    MYDOMAIN\USER1