The System.Web.Security.WindowsAuthenticationModule constructs a System.Web.Security.WindowsAuthenticationEventArgs object using the Windows identity supplied by IIS and the current System.Web.HttpContext and passes it to the WindowsAuthentication_OnAuthenticate event.

If IIS uses anonymous authentication, the WindowsAuthenticationEventArgs.Identity property is set to the identity returned by the System.Security.Principal.WindowsIdentity.GetAnonymous method.