Legacy fingerprint authentication for react native (Android only). Based on the deprecated FingerprintManger API. You probably want expo-local-authentication or react-native-fingerprint-scanner

Based heavily on react-native-fingerprint-android, but updated with:

• AndroidX support library use
• More FingerprintManager message codes
• Written with TypeScript & Kotlin
• Respects project settings for targetSdk & build.gradle config

The currently-maintained fingerprint/biometric auth libraries for React Native have all adopted the new BiometricPrompt. This is great!

However, some vendors (*cough* Samsung) have custom biometics overlays that lead to confusing UX on affected devices. In this case, it may be desirable to use the older FingerprintManger API.

• Android:
  • Requires Kotlin
• iOS:
  • No support planned
• react-native:
  • supported versions ">= 0.60.0"

This is a simplified version. There are a few more concerns you should be aware of. see 'Watch out!'
For the full version, see the example directory.

import Fingerprint from 'react-native-android-legacy-fingerprint';
import { ToastAndroid as Toast } from 'react-native';

(async() => {
  const hardware = await Fingerprint.isHardwareDetected();
  const permission = await Fingerprint.hasPermission();
  const enrolled = await Fingerprint.hasEnrolledFingerprints();

  if (!hardware || !permission || !enrolled) {
    let message = !enrolled ? 'No fingerprints registered.' : !hardware ? 'This device doesn\'t support fingerprint scanning.' : 'App has no permission.'
    Toast.show(message, Toast.SHORT);
    return;
  }

  try {
    await Fingerprint.authenticate(warning => {
        Toast.show(`Try again: ${warning.message}`, Toast.SHORT);
    });
  } catch(error) {
    Toast.show(`Authentication aborted: ${error.message}`, Toast.SHORT);
  }

  Toast.show("Auth successful!", Toast.SHORT);
})();

All functions & constants are static.

Starts authentication flow, with a optional callback for warning messages, instructing your user why authentication failed.
Returns a Promise.

Authentication resolves to a boolean indicating if the fingerprint was recognized and auth succeeded. If the result is false, the fingerprint was recognized but not valid.

Authentication has failed if the promise gets rejected.
Callback will receive a single parameter with the following structure: (example)

{
    "code": 1,
    "message": "The hardware is unavailable. Try again later."
}

This code will be match one of the following constants in the FingerprintAndroid module:

For more info on the constants, see Android FingerprintManager docs

warningCallback is the only and optional parameter to .authenticate().
If present, warningCallback gets called with a single parameter, a object with the following structure:

{
    "code": 1,
    "message": "Only acquired a partial fingerprint. Try again."
}

This code will be match one of the following constants in FingerprintAndroid:

For more info on the constants, see Android FingerprintManager docs

Tells you whether or not authentication is running or not.

Will check if android.permission.USE_FINGERPRINT is granted to this app. (should always return true if you add the permission to your AndroidManifest...)

Determine if there is at least one fingerprint enrolled.

Determine if fingerprint hardware is present and functional.

Manually cancel the authentication, this is required to follow the design principles in the design guidelines. When called this will trigger a rejection of the original authenticate promise.

React Native Fingerprint Android is mostly just a set of bindings to Android FingerprintManager.
Alas, it's very low level. You are still responsible for:

• Making sure the device has fingerprints enrolled by calling FingerprintAndroid.hasEnrolledFingerprints() (if you don't check this before starting authentication, any valid fingerprint will be accepted)
• Making sure your app has proper permissions setup (see installation guide below)
• Making sure device has supported hardware by calling FingerprintAndroid.isHardwareDetected()
• Making sure you display the correct icon, as defined by the design guidelines.
• Restarting authentication if screen turns off. (see example project for on an example on how to do that)

If you don't do any of the checks before calling FingerprintAndroid.authenticate, it will either directly fail, or your app will contain security vulnerabilities.