.NET MAUI Biometrics: Fingerprint & Face ID Guide

Still unlocking your apps with a four‑digit PIN? In 2025 that’s like locking Fort Knox with a paperclip. Let’s upgrade your security—and your CV—by wiring fingerprint and facial recognition into your .NET MAUI applications in less than a coffee break.

Why Bother With Biometrics?

User research consistently shows that people will choose convenience over security—unless they can enjoy both. Biometrics provide friction‑free sign‑in backed by hardware‑level protection, reducing password‑reset tickets and improving conversion rates. In short: you win, the user wins, the hacker loses.

Real‑world wins

• Kill the password reset loop – biometric fallback means fewer password emails.
• Regulatory brownie points – PSD2, HIPAA and friends love multi‑factor flows.
• Better UX metrics – our average time‑to‑first‑action dropped from 8 s to <3 s on iOS when we enabled Face ID.

Platform Support Cheat‑Sheet

Heads‑up: If you target older hardware, always implement a secure PIN fallback or skip biometrics when availability.CanAuthenticate returns false.

Setting Up the Project

1. Install the NuGet package

dotnet add package Oscore.Maui.Biometric

2. Wire up the service in MauiProgram.cs

using Oscore.Maui.Biometric;

builder
    .UseMauiApp<App>()
    .UseBiometricAuthentication()       // registers IBiometricAuthentication
    .ConfigureFonts(fonts =>
    {
        fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
    });

3. Add platform permissions

Android AndroidManifest.xml

<uses-permission android:name="android.permission.USE_BIOMETRIC" />
<uses-permission android:name="android.permission.USE_FINGERPRINT" android:maxSdkVersion="27" />

iOS Info.plist

<key>NSFaceIDUsageDescription</key>
<string>This app uses Face ID to keep your data safe and your life easy.</string>

Fingerprint Flow in Five Lines

Here’s the minimal page‑level code that greeted me during a code review—and passed with flying colours:

var biometric = BiometricAuthentication.Current;

var availability = await biometric.GetAvailabilityAsync();
if (!availability.CanAuthenticate)
    await DisplayAlert("Sorry", availability.GetErrorMessage(), "OK");

var result = await biometric.AuthenticateAsync(
    new BiometricAuthenticationRequest
    {
        Title = "Sign in",
        Description = "Scan your fingerprint"
    },
    CancellationToken.None);

if (result.Authenticated)
    await Shell.Current.GoToAsync("//Home");

Tip: cache the success in SecureStorage. Most apps skip the second scan until the next cold start.

Face ID & Windows Hello

Face authentication is the same API—no extra code! The OS decides whether to surface a face, fingerprint or PIN prompt.

// Works for Touch ID, Face ID, and Hello
var result = await biometric.AuthenticateAsync(
    new BiometricAuthenticationRequest
    {
        Title = "Verify it’s really you",
        NegativeText = "Use password instead"
    });

Custom Face Matching (advanced)

Need your own face database (e.g., factory attendance kiosks)? Plug in the Azure Face API or OpenCV:

1. Capture a selfie via MediaPicker.
2. Send to FaceClient.DetectWithStreamAsync.
3. Store faceId in your backend and compare with FaceClient.VerifyAsync.

Keep local copies encrypted; GDPR fines hurt more than broken builds.

UX Best Practices

• Show the OS dialog instantly after the button tap—no spinners.
• Explain why: users get suspicious if a random biometric sheet pops up.
• Fallback gracefully to password/PIN after three failed attempts.
• Dark mode: Windows Hello dropped infrared‑only support in June 2025, so ensure a visible‑light camera is present.

Security Pitfalls I’ve Stepped Into

1. Assuming authentication ≠ authorization. Re‑check server‑side tokens.
2. Caching indefinitely. Store the timestamp and re‑prompt after 12 h.
3. Forgetting screenshot protections: enable FLAG_SECURE on Android (Window.SetFlags).

Testing Across Platforms

• Android Studio Emulator → Extended controls › Fingerprint › Touch sensor to simulate scans.
• iOS Simulator → Device › Face ID › Enrolled.
• Windows → spoof Windows Hello with WindowsHelloSimulator.exe (comes with Windows SDK 10.1+).

Automate with UITest by triggering AuthenticateAsync() behind an #if DEBUG flag that bypasses the call and returns Success.

FAQ: Biometric Gotchas in MAUI

Conclusion: Ship It Securely—And Let Your Users Smile

You now have a battle‑tested recipe to add fingerprint and face authentication to any .NET MAUI app with just a NuGet, five lines of code, and a sprinkle of permissions. Users log in faster, your audit logs look cleaner, and your boss thinks you’re a magician. Ready to push to production? Do it—and drop a comment telling me how much time you saved.