Provides classes for retrieving the current Windows user and for interacting with Windows users and groups. Commonly Used Types: System.Security.Principal.WindowsIdentity System.Security.Principal.SecurityIdentifier System.Security.Principal.NTAccount System.Security.Principal.WindowsPrincipal System.Security.Principal.IdentityReference System.Security.Principal.IdentityNotMappedException System.Security.Principal.WindowsBuiltInRole System.Security.Principal.WellKnownSidType