What you are after is referred to as user impersonation for IIS...
System.Security.Principal.WindowsImpersonationContext impersonationContext;
impersonationContext =
((System.Security.Principal.WindowsIdentity)User.Identity).Impersonate();
impersonationContext.Undo();
You will find a really useful article here...
https://support.microsoft.com/en-us/kb/306158[
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