Add login to your .NET MAUI application

using Android.App;
using Android.Content;
using Android.Content.PM;

namespace MyMauiApp.Platforms.Android;

[Activity(NoHistory = true, LaunchMode = LaunchMode.SingleTop, Exported = true)]
[IntentFilter(new[] { Intent.ActionView },
              Categories = new[] { Intent.CategoryDefault, Intent.CategoryBrowsable },
              DataScheme = CALLBACK_SCHEME)]
public class WebAuthenticatorActivity : Microsoft.Maui.Authentication.WebAuthenticatorCallbackActivity
{
    const string CALLBACK_SCHEME = "myapp";
}

using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows.Input;
using Auth0.OidcClient;

namespace MyMauiApp.ViewModels;

public class MainPageViewModel : INotifyPropertyChanged
{
    private readonly Auth0Client _client;
    private string _name;
    private string _email;
    private bool _isAuthenticated;

    public event PropertyChangedEventHandler PropertyChanged;

    public string Name
    {
        get => _name;
        set { _name = value; OnPropertyChanged(); }
    }

    public string Email
    {
        get => _email;
        set { _email = value; OnPropertyChanged(); }
    }

    public bool IsAuthenticated
    {
        get => _isAuthenticated;
        set
        {
            _isAuthenticated = value;
            OnPropertyChanged();
            OnPropertyChanged(nameof(IsNotAuthenticated));
        }
    }

    public bool IsNotAuthenticated => !IsAuthenticated;

    public ICommand LoginCommand { get; }
    public ICommand LogoutCommand { get; }

    public MainPageViewModel(Auth0Client client)
    {
        _client = client;
        LoginCommand = new Command(async () => await LoginAsync());
        LogoutCommand = new Command(async () => await LogoutAsync());
    }

    private async Task LoginAsync()
    {
        var loginResult = await _client.LoginAsync();

        if (loginResult.IsError)
        {
            if (loginResult.Error == "UserCancel")
                return; // User closed the browser — not an error

            await Shell.Current.DisplayAlert("Login failed", loginResult.Error, "OK");
            return;
        }

        // Read user profile claims from the ID token
        Name = loginResult.User.FindFirst(c => c.Type == "name")?.Value;
        Email = loginResult.User.FindFirst(c => c.Type == "email")?.Value;
        IsAuthenticated = true;
    }

    private async Task LogoutAsync()
    {
        await _client.LogoutAsync();

        Name = null;
        Email = null;
        IsAuthenticated = false;
    }

    private void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}