Biometric Unlock in MAUI

How To Implement Biometric Unlock in MAUI

Use the Microsoft.Maui.ApplicationModel APIs with platform-native biometric services.

1. Add Microsoft.Maui.Essentials (already included in MAUI projects)

2. Check if biometrics are available

using Microsoft.Maui.ApplicationModel;

var result = await BiometricPrompt.Default.RequestAsync(new BiometricPromptRequest
{
    Title = "Unlock App",
    Description = "Use your face or fingerprint to unlock",
});
if (result.Authenticated)
{
    // Continue to app
}
else
{
    // Handle failure
}

This uses Face ID / Fingerprint / Windows Hello, depending on the device.

3. Run on App Launch or Protected Page

protected override async void OnAppearing()
{
    base.OnAppearing();
    var authResult = await AuthenticateUser();
    if (!authResult)
    {
        await DisplayAlert("Access Denied", "Biometric authentication failed.", "OK");
        System.Diagnostics.Process.GetCurrentProcess().Kill(); // Or navigate back
    }
}

 Platform Notes

 Android:

• Uses BiometricPrompt API (supports face, fingerprint, iris)

 iOS:

• Uses Face ID or Touch ID, depending on hardware

 Windows:

• Uses Windows Hello (face, fingerprint, PIN)

What It Does

• Prompts user for biometric authentication on app start

• Grants access if biometric is successful

• Exits or denies access if authentication fails

Step-by-Step Setup

✅ 1. Create a new MAUI App

dotnet new maui -n BiometricUnlockApp
cd BiometricUnlockApp

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✅ 2. Install Required Package (optional for Android)

.NET MAUI includes most features out of the box. No extra packages are required for biometrics via Microsoft.Maui.ApplicationModel.

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✅ 3. MainPage.xaml

<VerticalStackLayout Padding="30" Spacing="20">
    <Label Text="Biometric Unlock Demo" FontSize="32" HorizontalOptions="Center" />
    <Label x:Name="StatusLabel" Text="Authenticating..." FontSize="20" HorizontalOptions="Center" />
</VerticalStackLayout>

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✅ 4. MainPage.xaml.cs

using Microsoft.Maui.Controls;
using Microsoft.Maui.ApplicationModel;

namespace BiometricUnlockApp;

public partial class MainPage : ContentPage
{
    public MainPage()
    {
        InitializeComponent();
    }

    protected override async void OnAppearing()
    {
        base.OnAppearing();

        var isAvailable = await BiometricPrompt.Default.IsSupportedAsync();

        if (!isAvailable)
        {
            await DisplayAlert("Not Supported", "Biometric authentication is not available on this device.", "OK");
            StatusLabel.Text = "Biometric not available";
            return;
        }

        var result = await BiometricPrompt.Default.RequestAsync(new BiometricPromptRequest
        {
            Title = "Unlock App",
            Description = "Use your face, fingerprint, or PIN to unlock.",
            CancelTitle = "Cancel"
        });

        if (result.Authenticated)
        {
            StatusLabel.Text = "Access granted ✅";
        }
        else
        {
            StatusLabel.Text = "Access denied ❌";
            await DisplayAlert("Authentication Failed", "You could not be authenticated.", "Exit");
            System.Diagnostics.Process.GetCurrentProcess().Kill(); // Close the app
        }
    }
}

 Platform-Specific Configuration

✅ Android: AndroidManifest.xml

Add these inside <manifest>:

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

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✅ iOS: Info.plist

Add these inside <dict>:

<key>NSFaceIDUsageDescription</key>
<string>We use Face ID to unlock the app securely</string>

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✅ Windows: No config needed

Uses Windows Hello automatically.

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✅ Run and Test

• Android: Face unlock, fingerprint, or device credential (depending on device)

• iOS: Face ID or Touch ID

• Windows: Windows Hello (if available)