Xamarin with Auth0 and TouchID Authentication

MyViewController.cs

// https://github.com/auth0-community/auth0-xamarin-oidc-samples/tree/master/Quickstart/01-Login/iOS

using System;

using UIKit;
using Auth0.OidcClient;
using System.Text;
using LocalAuthentication;
using Foundation;
using Xamarin.Auth;
using System.Linq;

namespace iOSSample
{
	public partial class MyViewController : UIViewController
	{
      
		partial void LoginButton_TouchUpInside(UIButton sender)
		{
			Console.WriteLine("Partial method for LoginButton");
		}

		private Auth0Client _client;

		public MyViewController() : base("MyViewController", null)
		{
		}

		public override void ViewDidLoad()
		{
			base.ViewDidLoad();
			// Perform any additional setup after loading the view, typically from a nib.

			Console.WriteLine("ViewDidLoad");

			UserDetailsTextView.Text = String.Empty;

			LoginButton.TouchUpInside += LoginButton_TouchUpInside;  
		}

		public override void DidReceiveMemoryWarning()
		{
			base.DidReceiveMemoryWarning();
			// Release any cached data, images, etc that aren't in use.
		}


        /* Check whether a refresh tokens exists in KeyChain/KeyStore. */
		private string doesRefreshTokenExists(){
			
			var account = AccountStore.Create().FindAccountsForService("iOSSample").FirstOrDefault();
			return (account != null) ? account.Properties["Refresh Token"] : null;
		}

        /*
         * Store Refresh Token in KeyChain/KeyStore
         * https://github.com/xamarin/recipes/tree/master/Recipes/xamarin-forms/General/store-credentials#storing-account-information
         */
		private void saveRefreshToken(String refreshToken){
			// 
            Account account = new Account
            {
                // Client ID 
                Username = "{{CLIENT_ID}}"
            };

            account.Properties.Add("Refresh Token", refreshToken);
            AccountStore.Create().Save(account, "iOSSample");
		}

        /*
         * Authenticate with TouchID if available https://docs.microsoft.com/en-us/xamarin/ios/platform/touchid
         * @return boolean 
         */
		 
		private bool authenticateWithTouchID(){
			
            var context = new LAContext();
            NSError AuthError;
            var myReason = new NSString("Authenticate using TouchID.");

            if (context.CanEvaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, out AuthError))
            {
                var replyHandler = new LAContextReplyHandler((success, error) => {
                    this.InvokeOnMainThread(() => {
                        if (success)
                        {
                            Console.WriteLine("You logged in!");
                            //PerformSegue("AuthenticationSegue", this);
                        }
                        else
                        {
                            Console.WriteLine("Could not login!");
                            // Show fallback mechanism here
                        }
                    });
                });
                context.EvaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, myReason, replyHandler);
				return true;
            }
            else
            {
                Console.WriteLine("Device does not support TouchID!");
				return false;
            }
		}
        

        /* 
         * Login Button Pressed Action 
         * 
        */
		private async void LoginButton_TouchUpInside(object sender, EventArgs e)
		{
			
			var sb = new StringBuilder();
			var refreshToken = this.doesRefreshTokenExists();

			if (!string.IsNullOrWhiteSpace(refreshToken)){
				Console.WriteLine("Refresh Token found on Device: " + refreshToken);
				if (authenticateWithTouchID()){
					// https://github.com/IdentityModel/IdentityModel.OidcClient2/blob/dev/src/IdentityModel.OidcClient/Results/RefreshTokenResult.cs

					var loginWithRefreshTokenResult = await _client.RefreshTokenAsync(refreshToken);
                    
					if (loginWithRefreshTokenResult.IsError){
						sb.AppendLine("An error occurred during access token exchange with refresh token:");
						sb.AppendLine(loginWithRefreshTokenResult.Error);
					} else {
						// Got refresh Token here, Do something with it
						Console.WriteLine("Refresh token grant succeededed.");
						sb.AppendLine($"Access Token: {loginWithRefreshTokenResult.AccessToken}");
					}



				}
			} else {
				Console.WriteLine("Refresh Token NOT found on Device: " + refreshToken);
				loginAndGetRefreshToken();
			}

			UserDetailsTextView.Text = sb.ToString();

		}
        


		private async void loginAndGetRefreshToken(){

			var Options = new Auth0ClientOptions
            {
                Domain = "{{AUTH0_DOMAIN}}",
                ClientId = "{{CLIENT_ID}}",
                Scope = "openid profile offline_access",

            };

			_client = new Auth0Client(Options);

            var loginResult = await _client.LoginAsync();

            var sb = new StringBuilder();

            if (loginResult.IsError)
            {
                sb.AppendLine("An error occurred during login:");
                sb.AppendLine(loginResult.Error);
            }
            else
            {
                sb.AppendLine($"ID Token: {loginResult.IdentityToken}");
                sb.AppendLine($"Access Token: {loginResult.AccessToken}");
                sb.AppendLine($"Refresh Token: {loginResult.RefreshToken}");
                sb.AppendLine();
                sb.AppendLine("-- Claims --");
                foreach (var claim in loginResult.User.Claims)
                {
                    sb.AppendLine($"{claim.Type} = {claim.Value}");
                }
                
				saveRefreshToken(loginResult.RefreshToken);
            }

            UserDetailsTextView.Text = sb.ToString();
		}
	}
}