registro de usuarios asp.net core

public async Task<IActionResult> OnPostAsync(string returnUrl = null)
        {
            returnUrl = returnUrl ?? Url.Content("~/");
            if (ModelState.IsValid)
            {
                var user = new ApplicationUser { UserName = Input.Email, Email = Input.Email };
                var result = await _userManager.CreateAsync(user, Input.Password);
                if (result.Succeeded)
                {
                    _logger.LogInformation("User created a new account with password.");

                    var code = await _userManager.GenerateEmailConfirmationTokenAsync(user);
                    var callbackUrl = Url.Page(
                        "/Account/ConfirmEmail",
                        pageHandler: null,
                        values: new { userId = user.Id, code = code },
                        protocol: Request.Scheme);

                    await _emailSender.SendEmailAsync(Input.Email, "Confirm your email",
                        $"Please confirm your account by <a href='{HtmlEncoder.Default.Encode(callbackUrl)}'>clicking here</a>.");

                    await _signInManager.SignInAsync(user, isPersistent: false);



                }
                foreach (var error in result.Errors)
                {
                    ModelState.AddModelError(string.Empty, error.Description);
                }
                //Quiero añadir el rol del usuario si no hay usuarios SuperAdmin si hay usuarios sera User.
                //método que devuelva true o false solo necesito escribir el usuario y el rol que tiene en la tabla
                LUsuarios LUsers = new LUsuarios();
                int countUsers = await LUsers.CountUsers();
                if (countUsers == 0)
                {
                    var roleUser = new ApplicationUserRole { UserId = user.Id, RoleId = 1 };
                }
                else
                {
                    var roleUser0 = new ApplicationUserRole { UserId = user.Id, RoleId = 4 };
                }

            }
            // If we got this far, something failed, redisplay form
            return Page();
        }