How-To: Get Started with Authentication

Uno.Extensions.Authentication provides you with a consistent way to add authentication to your application. It is recommended to use one of the built in IAuthenticationService implementations. This tutorial will use the custom authorization to validate user credentials.

Step-by-steps

Important

This guide assumes you used the template wizard or dotnet new unoapp to create your solution. If not, it is recommended that you follow the instructions for creating an application from the template.

1. Basic Credential Checking

Install Uno.Extensions.Authentication into all projects

Append UseAuthentication to the IHostBuilder instance. The Login callback is used to verify the credentials. If the user is authenticated, the callback needs to return a non-empty dictionary of key-value pairs (this would typically contain tokens such as an access token and/or refresh token).

private IHost Host { get; }

protected override void OnLaunched(LaunchActivatedEventArgs args)
{
    var builder = this.CreateBuilder(args)
        .Configure(host => 
        {
            host
            .UseAuthentication(auth =>
                auth.AddCustom(custom =>
                    custom.Login(
                        async (sp, dispatcher, tokenCache, credentials, cancellationToken) =>
                        {
                            var isValid = credentials.TryGetValue("Username", out var username) && username == "Bob";
                            return isValid ? 
                            credentials : default;
                        })
            ));
        });
...

Update MainPage to accept input via TextBox with a binding expression to connect to the Username property on the view model. The Button is also bound to the Authenticate method.
```
<TextBox Text="{Binding Username, Mode=TwoWay}" />
<Button Content="Login"
        Click="{x:Bind ViewModel.Authenticate}" />
```

Update MainViewModel to accept an IAuthenticationService instance. Note that the LoginAsync method requires an IDispatcher instance to be supplied, so this is added as a dependency of the MainViewModel too.

public string? Username { get; set; }

private readonly IAuthenticationService _auth;
private readonly IDispatcher _dispatcher;

public MainViewModel(
    IDispatcher dispatcher,
    INavigator navigator,
    IAuthenticationService auth)
{
    _auth = auth;
    _dispatcher = dispatcher;
    _navigator = navigator;
}

public async Task Authenticate()
{
    if (await _auth.LoginAsync(_dispatcher, new Dictionary<string, string> { { "Username", Username ?? string.Empty } }, CancellationToken.None))
    {
        await _navigator.NavigateViewModelAsync<SecondViewModel>(this);
    }
}

Update the Start method in ShellViewModel to invoke Refresh, which will determine if there are valid credentials. If this returns true, can navigate directly to SecondViewModel, otherwise to the MainViewModel.

public async Task Start()
{
    if (await _auth.RefreshAsync(CancellationToken.None))
    {
        await Navigator.NavigateViewModelAsync<SecondViewModel>(this);
    }
    else
    {
        await Navigator.NavigateViewModelAsync<MainViewModel>(this);
    }
}

Update the "Second" route in App.xaml.host.cs to specify that it depends on the "Main" route. This will make sure that even if the app navigates directly to the SecondPage, the MainPage will be added to the backstack.

routes
    .Register(
        new RouteMap("", View: views.FindByViewModel<ShellViewModel>() ,
            Nested: new RouteMap[]
            {
                new RouteMap("Main", View: views.FindByViewModel<MainViewModel>()),
                new RouteMap("Second", View: views.FindByViewModel<SecondViewModel>(), DependsOn:"Main"),
            }));

Update SecondPage XAML to include a Button for logging out of the application. This will invoke the Logout method on the SecondViewModel.

At this point the application can be run and the user can enter a username and click the Login button. If the name is "Bob" they will be navigated to the SecondPage. If the application is restarted the application will automatically navigate to the SecondPage, since the user is still logged in.

The user is likely to want to logout of the application, the LogoutAsync method has to be called on the IAuthenticationService.
```
<Button Content="Logout"
        Click="{x:Bind ViewModel.Logout}" />
```

Add the Logout method to the SecondViewModel. In this case the SecondViewModel has been changed to a record, with properties for the Dispatcher and the IAuthenticationService.

public record SecondViewModel(IDispatcher Dispatcher, IAuthenticationService Auth)
{
    public async Task Logout()
    {
        await Auth.LogoutAsync(Dispatcher, CancellationToken.None);
    }
}

From this walk through you can see how the IAuthenticationService can be used to authenticate a user using a very simple check on the username. The Login, Refresh and Logout method can all be implemented in order to change the behavior of the application.

2. Invoking an Authentication Service

Add Uno.Extensions.Http.Refit package reference to Extensions.props

Add POCO objects to working with dummyjson.com

[Headers("Content-Type: application/json")]
public interface IDummyJsonEndpoint
{
    [Post("/auth/login")]
    Task<AuthResponse> Login(Credentials credentials, CancellationToken ct);
}

public class Credentials
{
    [JsonPropertyName("username")]
    public string? Username { get; init; }
    [JsonPropertyName("password")]
    public string? Password { get; init; }
}

public class AuthResponse
{
    [JsonPropertyName("token")]
    public string? Token { get; set; }
}

Add configuration for Refit endpoints

private IHost Host { get; }

protected override void OnLaunched(LaunchActivatedEventArgs args)
{
    var builder = this.CreateBuilder(args)
        .Configure(host => 
        {
            host
            .UseHttp((context, services) =>
                http.AddRefitClient<IDummyJsonEndpoint>(context)
            );
        });
...

Update appsettings.json to include a section that specifies the base Url for the Refit service. Note that the section name needs to match the interface (dropping the leading I) name. In this case the interface name is IDummyJsonEndpoint, so the configuration section is DummyJsonEndpoint
```
{
  "AppConfig": {
    "Title": "AuthSample"
  },
  "LocalizationConfiguration": {
    "Cultures": [ "en" ]
  },
  "DummyJsonEndpoint": {
    "Url": "https://dummyjson.com",
    "UseNativeHandler": true
  }
}
```

Add the UseAuthentication method to the InitializeHost method, this time using the AddCustom overload that accepts a type parameter. Instead of an IServiceProvider being passed into the Login callback, and instance of the IDummyJsonEndpoint will be provided.

private IHost Host { get; }

protected override void OnLaunched(LaunchActivatedEventArgs args)
{
    var builder = this.CreateBuilder(args)
        .Configure(host => 
        {
            host
            .UseAuthentication(auth =>
                auth.AddCustom<IDummyJsonEndpoint>(custom =>
                    custom.Login(
                        async (authService, dispatcher, tokenCache, credentials, cancellationToken) =>
                        {
                            var name = credentials.FirstOrDefault(x => x.Key == "Username").Value;
                            var password = credentials.FirstOrDefault(x => x.Key == "Password").Value;
                            var creds = new Credentials { Username = name, Password = password };
                            var authResponse = await authService.Login(creds, cancellationToken);
                            if (authResponse?.Token is not null)
                            {
                                credentials["AccessToken"] = authResponse.Token;
                                return credentials;
                            }
                            return default;
                        })
            ));
        });
...

In this case the Username and Password are extracted out of the credentials dictionary and added to an instance of the Credentials class (which we added earlier, along with the IDummyJsonEndpoint interface), which is passed to the Login method.

Update the MainPage to include a TextBox for entering the password:

<TextBox Text="{Binding Username, Mode=TwoWay}" />
<TextBox Text="{Binding Password, Mode=TwoWay}" />
<Button Content="Login"
        Click="{x:Bind ViewModel.Authenticate}" />

Update the Authenticate method on the MainViewModel to pass both username and password to the LoginAsync method

public async Task Authenticate()
{
    if (await _auth.LoginAsync(_dispatcher, 
                                new Dictionary<string, string> { 
                                    { nameof(Username), Username ?? string.Empty },
                                    { nameof(Password), Password ?? string.Empty }
                                }, CancellationToken.None))
    {
        await _navigator.NavigateViewModelAsync<SecondViewModel>(this);
    }
}

With this done, the application has changed from self-validating the username entered by the user, to using a back-end service to perform the validation.