can't grab the current user?

I remember back in the old days (asp before .net?) at a previous job we were able to grab the NT_ID for the current person accessing the sight.
 I'm trying to use
System.Security.Principal.WindowsIdentity.GetCurrent().Name

and am getting a generic user called 'NT AUTHORITY\NETWORK SERVICE' for everyone who visits the site.

What am i missing? the ...GetCurrent().Name works when i'm debugging local but not on the server.
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