Get current logged in user from Windows

Is there a way that I can get just the Username of the logged in user from Windows using Asp.Net? In classic ASP I remember using the System.Variables but that doesn't seem to work in .Net.

 I don't want to have to setup the Membership to look at AD. Since I'm making an Intranet App then the user will have already authenticated against our network. At that point I would like to just get the Username and check that against a table in SQL. If that username is there then I'll take them to my Main.aspx page and if not then I'll direct them to an error page letting them know they don't have aceess to the App.

 I've tried Sytem.Environment.Username, Request.ServerVariables("AUTH_USER"), and User.Identity.Name without any luck.

 Anyone know of an article or a way that I can easily find out the Windows Username of the current user?

 Thanks
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