public async Task <IActionResult> OnPostAsync(string returnUrl = null)
        {
            returnUrl = returnUrl ?? Url.Content("~/");

            if (ModelState.IsValid)
            {
                // This doesn't count login failures towards account lockout
                // To enable password failures to trigger account lockout, set lockoutOnFailure: true
                var result = await _signInManager.PasswordSignInAsync(Input.Email, Input.Password, Input.RememberMe, lockoutOnFailure : true);

                if (result.Succeeded)
                {
                    var user    = _user.FindWithEmail(Input.Email);
                    var counter = _shoppingCart.Count(c => c.ApplicationUserId == user.Id);
                    HttpContext.Session.SetInt32("Counter", counter);
                    _logger.LogInformation("User logged in.");
                    return(LocalRedirect(returnUrl));
                }
                if (result.RequiresTwoFactor)
                {
                    return(RedirectToPage("./LoginWith2fa", new { ReturnUrl = returnUrl, RememberMe = Input.RememberMe }));
                }
                if (result.IsLockedOut)
                {
                    _logger.LogWarning("User account locked out.");
                    return(RedirectToPage("./Lockout"));
                }
                else
                {
                    ModelState.AddModelError(string.Empty, "Invalid login attempt.");
                    return(Page());
                }
            }

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