Gets or sets the System.Security.Principal.IPrincipal object to be associated with the current request.
a System.Security.Principal.IPrincipal
You can use the FormsAuthenticationEventArgs.User property to set the System.Web.HttpContext.User property of the current System.Web.HttpContext to a custom System.Security.Principal.IPrincipal object.
If you do not specify a value for the FormsAuthenticationEventArgs.User property during the FormsAuthentication_OnAuthenticate event, the identity supplied by the forms authentication ticket in the cookie or URL is used.