Xamarin SDK

using System;

using Android.App;
using Android.Content.PM;
using Android.Runtime;
using Android.OS;
using Authgear.Xamarin;
using Xamarin.Forms;

namespace MyApp.Droid
{
    [Activity(NoHistory = true, LaunchMode = LaunchMode.SingleTop, Exported = true)]
    [IntentFilter(new[] { Android.Content.Intent.ActionView },
        Categories = new[] { Android.Content.Intent.CategoryDefault, Android.Content.Intent.CategoryBrowsable },
        DataScheme = "com.myapp.example")]
    public class WebAuthenticationCallbackActivity : Xamarin.Essentials.WebAuthenticatorCallbackActivity
    {
    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android">
  <!-- Other elements such <application> -->
  <queries>
    <intent>
      <action android:name="android.support.customtabs.action.CustomTabsService" />
    </intent>
  </queries>
</manifest>

using System;

using Android.App;
using Android.Content.PM;
using Android.Runtime;
using Android.OS;

using Xamarin.Forms;
using Authgear.Xamarin;

namespace MyApp.Droid
{
    public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
    {
        protected override void OnCreate(Bundle savedInstanceState)
        {
            // ...

            var authgear = new AuthgearSdk(this, new AuthgearOptions
            {
                ClientId = CLIENT_ID,
                AuthgearEndpoint = ENDPOINT
            });
            DependencyService.RegisterSingleton<AuthgearSdk>(authgear);
            LoadApplication(new App());

            // ...
        }

        // other methods are omitted for brevity.
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <!-- other entries ... -->
        <key>CFBundleURLTypes</key>
        <array>
          <dict>
            <key>CFBundleURLName</key>
            <string>com.myapp.example://host/path</string>

            <key>CFBundleURLSchemes</key>
            <array>
              <string>com.myapp.example</string>
            </array>

            <key>CFBundleTypeRole</key>
            <string>Editor</string>
          </dict>
        </array>
</dict>
</plist>

using Xamarin.Essentials;
using Xamarin.Forms;
using Authgear.Xamarin;

namespace MyApp.iOS
{
    [Register("AppDelegate")]
    public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
    {
        public override bool FinishedLaunching(UIApplication app, NSDictionary options)
        {
            global::Xamarin.Forms.Forms.Init();
            var authgear = new AuthgearSdk(app, new AuthgearOptions
            {
                ClientId = CLIENT_ID,
                AuthgearEndpoint = ENDPOINT
            });
            DependencyService.RegisterSingleton<AuthgearSdk>(authgear);
            LoadApplication(new App());

            return base.FinishedLaunching(app, options);
        }

        public override bool OpenUrl(UIApplication app, NSUrl url, NSDictionary options)
        {
            return Xamarin.Essentials.Platform.OpenUrl(app, url, options);
        }

        public override bool ContinueUserActivity(UIApplication application, NSUserActivity userActivity, UIApplicationRestorationHandler completionHandler)
        {
            if (Xamarin.Essentials.Platform.ContinueUserActivity(application, userActivity, completionHandler))
                return true;
            return base.ContinueUserActivity(application, userActivity, completionHandler);
        }
    }
}

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="testauthgear.MainPage">

    <StackLayout>
        <Frame BackgroundColor="#2196F3" Padding="24" CornerRadius="0">
            <Label Text="Welcome to Xamarin.Forms!" HorizontalTextAlignment="Center" TextColor="White" FontSize="36"/>
        </Frame>
        <Button Text="Configure" Clicked="Configure_Clicked" />
        <Button Text="Authenticate" Clicked="Authenticate_Clicked"/>
    </StackLayout>

</ContentPage>

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using Authgear.Xamarin;

namespace MyApp
{
    public partial class MainPage : ContentPage
    {
        private AuthgearSdk authgear;


        public MainPage()
        {
            InitializeComponent();
            authgear = DependencyService.Get<AuthgearSdk>();
        }

        async void Configure_Clicked(object sender, EventArgs e)
        {
            // You must configure the instance before use.
            // Typically you should do this once on app launch.
            await authgear.ConfigureAsync();
        }

        async void Authenticate_Clicked(object sender, EventArgs e)
        {
            var userInfo = await authgear.AuthenticateAsync(new AuthenticateOptions
            {
                RedirectUri = REDIRECT_URI
            });
        }
    }
}

// value can be NoSession or Authenticated
// After Authgear.ConfigureAsync, it only reflects local state.
var sessionState = authgear.SessionState;

if (sessionState == SessionState.Authenticated)
{
    try
    {
        var userInfo = await authgear.FetchUserInfoAsync();
        // sessionState is now up to date
    }
    catch (Exception ex)
    {
        // sessionState is now up to date
        // it will change to NoSession if the session is invalid
    }
}

await authgear.LogoutAsync();

await authgear.RefreshAccessTokenIfNeededAsync();
// Access token is ready to use
// AccessToken can be string or undefined
// It will be empty if user is not logged in or session is invalid
var accessToken = authgear.AccessToken;
var client = GetHttpClient();  // Get the re-used http client of your app, as per recommendation.
var httpRequestMessage = new HttpRequestMessage(myHttpMethod, myUrl);
httpRequestMessage.Headers.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);