Using FormsAuthentication_OnAuthenticate in global.asax.cs

I would like to use roles and membership without using the ASP.net membership. As a result, I use the FormsAuthentication_OnAuthenticate in global.asax.cs instead of

using the conventional Login_Authenticate.

When I was debugging this code, I found that the web application keeps authenticating in global.asax.cs

Code is as follows:

protected void FormsAuthentication_OnAuthenticate(Object sender, FormsAuthenticationEventArgs e)
        {
            if (FormsAuthentication.CookiesSupported == true)
            {
                if (Request.Cookies[FormsAuthentication.FormsCookieName] != null)
                {
                    try
                    {
                        //let us take out the username now
                        string username = FormsAuthentication.Decrypt(Request.Cookies[FormsAuthentication.FormsCookieName].Value).Name;

                        //let us extract the roles from our own custom cookie
                                                string exmsg = "";
                        bool bAllUsersInCharge = false;
                        bool bEnabled = false;

                        string roles = GetUserRole(username, out exmsg, out bEnabled, out bAllUsersInCharge);

                        //Let us set the Pricipal with our user specific details
                        e.User = new System.Security.Principal.GenericPrincipal(
                          new System.Security.Principal.GenericIdentity(username, "Forms"), roles.Split(';'));

                    }
                    catch (Exception ex)
                    {
                        string msg = ex.Message;
                        //somehting went wrong
                    }
                }
                else
                {
                    e.User = null;
                  //  Response.Redirect("~/Login.aspx");

                }
            }
        }