error when logging in with ASP.NET Core Identity in WPF application

Body: I am developing a WPF application using ASP.NET Core Identity for user authentication. The signup process works correctly, and I can see the user in my database after creating an account. However, when I try to log in with the correct username and password, I get the following error message in a popup:

An error occurred: Value cannot be null (Parameter 'provider')

Here is the relevant code for my App.xaml.cs :

using CISN_app.Data;
using CISN_app.Models;
using CISN_app.Services;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using System.Windows;

namespace CISN_app
{
    public partial class App : Application
    {
        private ServiceProvider _serviceProvider = null!;

        protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);

            var services = new ServiceCollection();
            ConfigureServices(services);
            _serviceProvider = services.BuildServiceProvider();

            var loginWindow = _serviceProvider.GetRequiredService<Login>();
            loginWindow.Show();
        }

        private void ConfigureServices(IServiceCollection services)
        {
            services.AddDbContext<AppDbContext>(options =>
                options.UseSqlServer("Data Source=my_server;Initial Catalog=my_database;Integrated Security=True;Connect Timeout=30;Encrypt=False;Trust Server Certificate=False;Application Intent=ReadWrite;Multi Subnet Failover=False"));

            services.AddLogging();
            services.AddIdentity<User, IdentityRole>(options =>
            {
                options.Password.RequireDigit = true;
                options.Password.RequiredLength = 6;
                options.Password.RequireNonAlphanumeric = true;
                options.Password.RequireUppercase = false;
                options.Password.RequireLowercase = false;
                options.Password.RequiredUniqueChars = 1;
                options.SignIn.RequireConfirmedAccount = false; 
            })
            .AddEntityFrameworkStores<AppDbContext>()
            .AddDefaultTokenProviders();

            services.AddHttpContextAccessor();

            services.AddTransient<Login>();
            services.AddTransient<SignUp>();
            services.AddScoped<SignInManager<User>, CustomSignInManager>(); 
        }
    }
}

And here is the custom SignInManager implementation:

using CISN_app.Models;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Identity;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using System.Threading.Tasks;

namespace CISN_app.Services
{
    public class CustomSignInManager : SignInManager<User>
    {
        public CustomSignInManager(UserManager<User> userManager,
                                   IUserClaimsPrincipalFactory<User> claimsFactory,
                                   IOptions<IdentityOptions> optionsAccessor,
                                   ILogger<SignInManager<User>> logger,
                                   IAuthenticationSchemeProvider schemes,
                                   IUserConfirmation<User> confirmation)
            : base(userManager, null, claimsFactory, optionsAccessor, logger, schemes, confirmation)
        {
        }

        public override Task<SignInResult> PasswordSignInAsync(string userName, string password, bool isPersistent, bool lockoutOnFailure)
        {
            return base.PasswordSignInAsync(userName, password, isPersistent, lockoutOnFailure);
        }
    }
}

Here is the LoginButton_Click method:

private async void LoginButton_Click(object sender, RoutedEventArgs e)
{
    string username = UsernameTextBox.Text;
    string password = PasswordBox.Password;

    if (string.IsNullOrEmpty(username) || string.IsNullOrEmpty(password))
    {
        MessageBox.Show("Please enter both username and password.", "Login Error", MessageBoxButton.OK, MessageBoxImage.Warning);
        return;
    }

    var context = new DefaultHttpContext();
    _httpContextAccessor.HttpContext = context;

    try
    {
        var result = await _signInManager.PasswordSignInAsync(username, password, false, false).ConfigureAwait(false);
        if (!result.Succeeded)
        {
            MessageBox.Show("Invalid username or password.", "Login Error", MessageBoxButton.OK, MessageBoxImage.Error);
        }
        else
        {
            Application.Current.Dispatcher.Invoke(() =>
            {
                Menu menuWindow = new Menu();
                menuWindow.Show();
                this.Close();
            });
        }
    }
    catch (ArgumentNullException ex)
    {
        MessageBox.Show($"An error occurred: {ex.Message}", "Login Error", MessageBoxButton.OK, MessageBoxImage.Error);
    }
}