What is the purpose of Application_AuthenticateRequest in global.asax

Hi,


in the log.aspx I used this function to authenticate.
protected void AuthenticateUser(/*string roles*/)
    {
        //Providing the FormsAuthenticationTicket "Ticket" to the authenticated user which contains version, username, entry datetime and expire date time, userdata and cookie path
        FormsAuthentication.Initialize();
        FormsAuthenticationTicket Ticket = new FormsAuthenticationTicket(1, LoginForm.UserName.Trim(), DateTime.Now,
                                                            &nb ...