FormsAuthentication - How to not expire session

I've been searching some way that my session will never expire, unless the user logs out.

My code is like this, I am obliged to inform the validity of the session:

public void CreateAuthorizeTicket(string userId, string roles)
{

  var authTicket = new FormsAuthenticationTicket(
  1,
  userId,  // Id do usuário é muito importante
  DateTime.Now,
  DateTime.Now.AddMinutes(100),  // validade min session
  false,   // Se você deixar true, o cookie ficará no PC do usuário
  roles);

  string encrypetedTicket = FormsAuthentication.Encrypt(authTicket);
  FormsAuthentication.SetAuthCookie(encrypetedTicket, false);

  var cookie = new HttpCookie(FormsAuthentication.FormsCookieName, 
  FormsAuthentication.Encrypt(authTicket));
  Response.Cookies.Add(cookie);
}

Global.asax.cs:

protected void Application_AuthenticateRequest(Object sender, EventArgs e)
{
   if (HttpContext.Current.User == null) return;
   if (!HttpContext.Current.User.Identity.IsAuthenticated) return;
   if (HttpContext.Current.User.Identity is FormsIdentity)
   {
     var id = (FormsIdentity)HttpContext.Current.User.Identity;
     FormsAuthenticationTicket ticket = id.Ticket;
     string userData = ticket.UserData;
     string[] roles = userData.Split(',');
     HttpContext.Current.User = new GenericPrincipal(id, roles);
   }
}