Xamarin and MvvMCross plugin for authenticate a user via fingerprint sensor
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README.md

Fingerprint plugin for Xamarin

Xamarin and MvvMCross plugin for accessing the fingerprint sensor.

Type Stable Pre release
vanilla NuGet NuGet
MvvmCross NuGet NuGet

Changelog

Support

The plugin supports the listed platforms.

If you like the quality and code you can support me Donate Thanks!

Platform Version
Xamarin.Android 4.4
Xamarin.iOS 8.0
Xamarin.Mac 10.12
Windows UWP 10

Setup

iOS

Add NSFaceIDUsageDescription to your Info.plist to describe the reason your app uses Face ID. (see Documentation). Otherwise the App will crash when you start a Face ID authentication on iOS 11.3+.

<key>NSFaceIDUsageDescription</key>
<string>Need your face to unlock secrets!</string>

Android

Set Target SDK version

The target SDK version has to be >= 6.0. I recomment to use always the latest stable SDK version, if possible. You can set the target SDK version in your Android project properties.

Request the permission in AndroidManifest.xml

The first line is for the standard Android API and the second for Samsung devices using the Pass API.

<uses-permission android:name="android.permission.USE_FINGERPRINT" />
<uses-permission android:name="com.samsung.android.providers.context.permission.WRITE_USE_APP_FEATURE_SURVEY" />

Set the resolver of the current Activity

Skip this, if you use the MvvMCross Plugin or don't use the dialog.

We need the current activity to display the dialog. You can use the Current Activity Plugin from James Montemagno or implement your own functionality to retrieve the current activity. See Sample App for details.

CrossFingerprint.SetCurrentActivityResolver(() => CrossCurrentActivity.Current.Activity);

Usage

Example

vanilla

var result = await CrossFingerprint.Current.AuthenticateAsync("Prove you have fingers!");
if (result.Authenticated)
{
    // do secret stuff :)
}
else
{
    // not allowed to do secret stuff :(
}

using MvvMCross

var fpService = Mvx.Resolve<IFingerprint>(); // or use dependency injection and inject IFingerprint

var result = await fpService.AuthenticateAsync("Prove you have mvx fingers!");
if (result.Authenticated)
{
    // do secret stuff :)
}
else
{
    // not allowed to do secret stuff :(
}

Xamarin University public lecture

Xamarin University public lecture

API

The API is defined by the IFingerprint interface:

/// <summary>
/// Checks the availability of fingerprint authentication.
/// Checks are performed in this order:
/// 1. API supports accessing the fingerprint sensor
/// 2. Permission for accessint the fingerprint sensor granted
/// 3. Device has sensor
/// 4. Fingerprint has been enrolled
/// <see cref="FingerprintAvailability.Unknown"/> will be returned if the check failed 
/// with some other platform specific reason.
/// </summary>
/// <param name="allowAlternativeAuthentication">
/// En-/Disables the use of the PIN / Passwort as fallback.
/// Supported Platforms: iOS, Mac
/// Default: false
/// </param>
Task<FingerprintAvailability> GetAvailabilityAsync(bool allowAlternativeAuthentication = false);

/// <summary>
/// Checks if <see cref="GetAvailabilityAsync"/> returns <see cref="FingerprintAvailability.Available"/>.
/// </summary>
/// <param name="allowAlternativeAuthentication">
/// En-/Disables the use of the PIN / Passwort as fallback.
/// Supported Platforms: iOS, Mac
/// Default: false
/// </param>
/// <returns><c>true</c> if Available, else <c>false</c></returns>
Task<bool> IsAvailableAsync(bool allowAlternativeAuthentication = false);

/// <summary>
/// Requests the authentication.
/// </summary>
/// <param name="reason">Reason for the fingerprint authentication request. Displayed to the user.</param>
/// <param name="cancellationToken">Token used to cancel the operation.</param>
/// <returns>Authentication result</returns>
Task<FingerprintAuthenticationResult> AuthenticateAsync(string reason, CancellationToken cancellationToken = default(CancellationToken));

/// <summary>
/// Requests the authentication.
/// </summary>
/// <param name="authRequestConfig">Configuration of the dialog that is displayed to the user.</param>
/// <param name="cancellationToken">Token used to cancel the operation.</param>
/// <returns>Authentication result</returns>
Task<FingerprintAuthenticationResult> AuthenticateAsync(AuthenticationRequestConfiguration authRequestConfig, CancellationToken cancellationToken = default(CancellationToken));

The returned FingerprintAuthenticationResult contains information about the authentication.

/// <summary>
/// Indicatates whether the authentication was successful or not.
/// </summary>
public bool Authenticated { get { return Status == FingerprintAuthenticationResultStatus.Succeeded; } }

/// <summary>
/// Detailed information of the authentication.
/// </summary>
public FingerprintAuthenticationResultStatus Status { get; set; }

/// <summary>
/// Reason for the unsucessful authentication.
/// </summary>
public string ErrorMessage { get; set; }

Example

vanilla

var result = await CrossFingerprint.Current.AuthenticateAsync("Prove you have fingers!");
if (result.Authenticated)
{
    // do secret stuff :)
}
else
{
    // not allowed to do secret stuff :(
}

using MvvMCross

var fpService = Mvx.Resolve<IFingerprint>(); // or use dependency injection and inject IFingerprint

var result = await fpService.AuthenticateAsync("Prove you have mvx fingers!");
if (result.Authenticated)
{
    // do secret stuff :)
}
else
{
    // not allowed to do secret stuff :(
}

mocking in unit tests

//Create mock with LigthMock (http://www.lightinject.net/)
var mockFingerprintContext = new MockContext<IFingerprint>();
var mockFingerprint = new CrossFingerprintMock(mockFingerprintContext);

mockFingerprintContext.Current = mockFingerprint;

iOS

Limitations

You can't create a custom dialog. The standard iOS Dialog will be shown.

iOS 9+ only
  • cancelable programmatically with passed CancellationToken
  • custom fallback button title
iOS 10+ only
  • custom cancel button title

Android

Limitations

You can't use the alternative authentication method.

Configuration

If you don't like the default dialog, you can easily customize it. You have to inherit from FingerprintDialogFragment e.g. like:

public class MyCustomDialogFragment : FingerprintDialogFragment
{
    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        var view = base.OnCreateView(inflater, container, savedInstanceState);
        view.Background = new ColorDrawable(Color.Magenta); // make it fancyyyy :D
        return view;
    }
}

And somewhere in your code set your custom dialog fragment:

CrossFingerprint.SetDialogFragmentType<MyCustomDialogFragment>();

UWP

Limitations

You can't use the alternative authentication method.

Testing on Simulators

iOS

Controlling the sensor on the iOS Simulator

With the Hardware menu you can

  • Toggle the enrollment status
  • Trigger valid ( M) and invalid ( N) fingerprint sensor events

Android

  • start the emulator (Android >= 6.0)
  • open the settings app
  • go to Security > Fingerprint, then follow the enrollment instructions
  • when it asks for touch
  • open command prompt
  • telnet 127.0.0.1 <emulator-id> (adb devices prints "emulator-<emulator-id>")
  • finger touch 1
  • finger touch 1

Sending fingerprint sensor events for testing the plugin can be done with the telnet commands, too.

Note for Windows users: You have to enable telnet: Programs and Features > Add Windows Feature > Telnet Client

Nice to know

ProGuard

If you use the plugin with Link all, Release Mode and ProGuard enabled, you may have to add the follwoing rules to your proguard.cfg.

-dontwarn com.samsung.**
-keep class com.samsung.** {*;}

Contribution

+