Excellent ASP.NET Identity Matrix reference
Historical article · Originally published September 26, 2003; technical details may be outdated.
I remember reading about this somewhere, and came across this great reference! Hurray for the MS patterns and practices team!
Summary:
This document provides tables that illustrate, for a range of IIS authentication settings, the resultant identity that is obtained from each of the variables that maintain an IPrincipal and/or IIdentity object.