public async Task <IActionResult> Register(int id)
        {
            var ceClass = _repo.GetClassById(id);

            if (ceClass.RegisteredAgents.Count() < ceClass.MaxSize)
            {
                var currentUser = await _userManager.GetUserAsync(HttpContext.User);

                ceClass.RegisteredAgents.Add(new RegisteredAgent {
                    AppUser = currentUser, CEClass = ceClass
                });

                var emailRegisterViewModel = new EmailRegisterViewModel(ceClass);

                _emailSender.SendEmailAsync("*****@*****.**", $"Registered for {ceClass.ClassTitle}", "RegisteredClass", emailRegisterViewModel);

                _repo.SaveChanges();
            }

            return(Redirect("/CEClass/Classes"));
        }