Page.cs

public class LoginModel : PageModel
{
    // Code Omitted

    [BindProperty]
    public InputModel Input { get; set; }

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

        if (ModelState.IsValid)
        {
            var result = await _signInManager.PasswordSignInAsync(Input.Email, Input.Password, false, true);
            if (result.Succeeded)
            {
                _logger.LogInformation("User logged in.");
                await TransferAnonymousBasketToUserAsync(Input.Email);
                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();
            }
        }

        return Page();
    }

    private async Task TransferAnonymousBasketToUserAsync(string userName)
    {
        if (Request.Cookies.ContainsKey(Constants.BASKET_COOKIENAME))
        {
            var anonymousId = Request.Cookies[Constants.BASKET_COOKIENAME];
            if (Guid.TryParse(anonymousId, out var _))
            {
                await _basketService.TransferBasketAsync(new Username(anonymousId), new Username(userName));
            }
            Response.Cookies.Delete(Constants.BASKET_COOKIENAME);
        }
    }
}