Android BiometricsService using BiometricPrompt

BiometricsService.cs

using System;
using System.Threading.Tasks;
using Android;
using Android.App;
using Android.Content;
using Android.Content.PM;
using Android.Hardware.Biometrics;
using Android.OS;
using Android.Support.V4.App;
using Android.Support.V4.Hardware.Fingerprint;
using Java.Lang;

namespace DIPS.Xamarin.Essentials.Android.Authentication {
    internal class BiometricsService : BiometricPrompt.AuthenticationCallback, IBiometricsService
    {
        internal static Activity MainActivity;
        private TaskCompletionSource<BiometricsResponse> m_taskCompletionSource;

        public Task<BiometricsResponse> Authenticate()
        {
            m_taskCompletionSource = new TaskCompletionSource<BiometricsResponse>();

            if (!BiometricUtils.IsBiometricPromptEnabled())
            {
                m_taskCompletionSource.SetResult(new BiometricsResponse(BiometricsStatus.NotAvailable, "BiometricPrompt not available"));
            }

            if (!BiometricUtils.IsSdkVersionSupported())
            {
                m_taskCompletionSource.SetResult(new BiometricsResponse(BiometricsStatus.NotAvailable, "Android version is lower than Marshmallow, fingerprint authentication is only supported from Android 6.0"));
            }

            if (!BiometricUtils.IsHardwareSupported(MainActivity))
            {
                m_taskCompletionSource.SetResult(new BiometricsResponse(BiometricsStatus.NotAvailable, "The device does not have fingerprint sensors"));
            }

            if (!BiometricUtils.IsFingerprintAvailable(MainActivity))
            {
                m_taskCompletionSource.SetResult(new BiometricsResponse(BiometricsStatus.NotAvailable, "No fingerprints have been enrolled. Please go to settings and add fingerprints."));
            }

            var biometricPrompt = new BiometricPrompt.Builder(MainActivity).SetTitle("title").SetDescription("description")
                .SetSubtitle("subtitle").SetNegativeButton("Cancel", MainActivity.MainExecutor, new DialogListener(OnCancel)).Build();
            var cancellationSignal = new CancellationSignal();
            biometricPrompt.Authenticate(
                cancellationSignal,
                MainActivity.MainExecutor,
                this);


            return m_taskCompletionSource.Task;
        }

        public override void OnAuthenticationError(BiometricErrorCode errorCode, ICharSequence errString)
        {
            if (m_taskCompletionSource.Task.IsCompleted)
                return;
            m_taskCompletionSource.SetResult(new BiometricsResponse(BiometricsStatus.UnknownError, errString != null ? errString.ToString() : "Unknown error"));
            base.OnAuthenticationError(errorCode, errString);
        }

        public override void OnAuthenticationFailed()
        {
            base.OnAuthenticationFailed();
        }

        public override void OnAuthenticationHelp(BiometricAcquiredStatus helpCode, ICharSequence helpString)
        {
            base.OnAuthenticationHelp(helpCode, helpString);
        }

        public override void OnAuthenticationSucceeded(BiometricPrompt.AuthenticationResult result)
        {
            if (m_taskCompletionSource.Task.IsCompleted) return;
            m_taskCompletionSource.SetResult(new BiometricsResponse(BiometricsStatus.Succeeded, "Biometrics or pin-code succeeded"));
            base.OnAuthenticationSucceeded(result);
        }


        private void OnCancel()
        {
            if (m_taskCompletionSource.Task.IsCompleted)
                return;
            m_taskCompletionSource.TrySetResult(new BiometricsResponse(BiometricsStatus.Canceled, "The user has canceled biometrics or pin-code"));
        }
    }

    public class DialogListener : Java.Lang.Object, IDialogInterfaceOnClickListener
    {
        private Action m_onCancel;

        public DialogListener(Action onCancel)
        {
            m_onCancel = onCancel;
        }

        public void OnClick(IDialogInterface dialog, int which)
        {
            m_onCancel.Invoke();
        }
    }
    public class BiometricUtils
    {

        public static bool CheckAll(Context context) =>
            IsBiometricPromptEnabled() && IsSdkVersionSupported() && IsSdkVersionSupported() && IsHardwareSupported(context) &&
            IsFingerprintAvailable(context) && IsPermissionGranted(context);
        public static bool IsBiometricPromptEnabled()
        {
            return (Build.VERSION.SdkInt >= Build.VERSION_CODES.P);
        }


        /// <summary>
        ///  Condition I: Check if the android version in device is greater than
        ///  Marshmallow, since fingerprint authentication is only supported
        /// from Android 6.0.
        ///  Note: If your project's minSdkversion is 23 or higher,
        ///   then you won't need to perform this check.
        /// </summary>
        /// <returns></returns>
        public static bool IsSdkVersionSupported() => (Build.VERSION.SdkInt >= BuildVersionCodes.M);

        /// <summary>
       /// Condition II: Check if the device has fingerprint sensors.
       /// Note: If you marked android.hardware.fingerprint as something that
       /// your app requires (android:required= "true"), then you don't need
       /// to perform this check.
       /// </summary>
       /// <param name="context"></param>
       /// <returns></returns>
        public static bool IsHardwareSupported(Context context) => FingerprintManagerCompat.From(context).IsHardwareDetected;

       /// <summary>
        /// Condition III: Fingerprint authentication can be matched with a 
        /// registered fingerprint of the user. So we need to perform this check</summary>
        /// in order to enable fingerprint authentication<param name="context"></param>
        /// <returns></returns>
        public static bool IsFingerprintAvailable(Context context) => FingerprintManagerCompat.From(context).HasEnrolledFingerprints;

       /// <summary>
        /// Condition IV: Check if the permission has been added to
        /// the app. This permission will be granted as soon as the user</summary>
        /// installs the app on their device.<param name="context"></param>
        /// <returns></returns>
        public static bool IsPermissionGranted(Context context)
       {
           return ActivityCompat.CheckSelfPermission(context, Manifest.Permission.UseFingerprint) == Permission.Granted &&
                  ActivityCompat.CheckSelfPermission(context, Manifest.Permission.UseBiometric) == Permission.Granted;
       }
    }
    
    internal interface IBiometricsService {
        Task<BiometricsResponse> Authenticate();
    }

    internal class BiometricsResponse
    {
        public BiometricsStatus Status { get; }
        public string Message { get; }

        public BiometricsResponse(BiometricsStatus status, string message)
        {
            Status = status;
            Message = message;
        }
    }

    public enum BiometricsStatus
    {
        Unknown,
        Succeeded,
        FallbackRequested,
        Failed,
        Canceled,
        TooManyAttempts,
        UnknownError,
        NotAvailable,
        Denied,
    }
}