Implementing Biometric Authentication In .NET MAUI

<uses-permission android:name="android.permission.USE_FINGERPRINT" />

using Plugin.Fingerprint;

CrossFingerprint.SetCurrentActivityResolver(() => this);

In iOS authentication is simpler. You just have to add the “NSFaceIDUsageDescription” to the Info.plist file to describe the reason why our application will use Face ID (see Documentation). Otherwise, the app will crash when you initiate a Face ID authentication on iOS 11.3+.

<key>NSFaceIDUsageDescription</key>
<string>Need your face to unlock magic things</string>

Note: If you have any questions about how to implement this, I recommend that you follow the guide on GitHub to learn more about how to configure it for your .NET MAUI project. It's worth mentioning that the guide is currently in the Maui support branch, so if the link doesn't work, it's already been merged and you can use the link provided above.

MauiProgram.cs

Finally, and before going to modify our XAML and add the main functionality, in the MauiProgram.cs file we must add the following lines:

builder.Services.AddSingleton<MainPage>();
builder.Services.AddSingleton(typeof(IFingerprint), CrossFingerprint.Current);

Staying as follows:

XAML

Next, add a button with a click handler (or modify the one the solution created for us if the project is new):

<Button 
      Text="Authenticate"
      FontAttributes="Bold"
      SemanticProperties.Hint="Click to authenticate with your fingerprint"
      Clicked="OnBiometricClicked"
      HorizontalOptions="Center" />

Next, we must add the corresponding using:

using Plugin.Fingerprint.Abstractions;

Then declare the IFingerprint interface:

private readonly IFingerprint fingerprint;

The same as passed as parameter:

public MainPage(IFingerprint fingerprint)

After that, we will declare inside the MainPage:

InitializeComponent();
this.fingerprint = fingerprint;

Now, inside the "OnBiometricClicked" event handler, in the code-behind add the following code. When you click the button, it will ask you to authenticate via fingerprint:

private async void OnBiometricClicked(object sender, EventArgs e)
{
    var request = new AuthenticationRequestConfiguration("Validate that you have fingers", "Because without them you will not be able to access");
    var result = await fingerprint.AuthenticateAsync(request);
    if (result.Authenticated)
    {
        await DisplayAlert("Authenticate!", "Access Granted", "OK");
    }
    else
    {
        await DisplayAlert("Unauthenticated", "Access Denied", "OK");
    }
}

And voila, that's it!

Result / Output - Android

As always, I've provided a code example on my GitHub below, which you can check out if you'd like.

Summary

I hope this little article has given you enough information to apply such control in your .NET MAUI applications and see the expected results.

I invite you to leave a comment if you want me to give more details about anything in this article.

More Information: GitHub Xamarin-Fingerprint

Happy coding!