Biometrics

Install

npx expo install expo-local-authentication

import { Biometrics } from '@ng-native/expo/biometrics';

The smallest thing that works

import { Component, inject } from '@angular/core';
import { Biometrics } from '@ng-native/expo/biometrics';

@Component({
  selector: 'app-wallet',
  template: '<pressable (press)="unlock()"><text>Unlock</text></pressable>',
})
export class Wallet {
  private readonly biometrics = inject(Biometrics);

  protected async unlock(): Promise<void> {
    if (!(await this.biometrics.available())) return;
    const result = await this.biometrics.authenticate('Unlock your wallet');
    if (result.success) this.reveal();
  }

  private reveal(): void {}
}

Checking and asking

• available() resolves to whether there is a sensor and something enrolled on it - whether asking can succeed at all. Check it before showing a "Use Face ID" button.
• kinds() resolves to the kinds the device has - 'fingerprint', 'face', 'iris' - so a button can say "Use Face ID" rather than the generic "Use biometrics".
• authenticate(message, options) shows the system prompt with message as the reason, and resolves to { success: true } or { success: false, error }, where error is the platform's own reason: 'user_cancel', 'lockout', 'not_enrolled' and so on. options is expo-local-authentication's own LocalAuthenticationOptions (minus promptMessage, which message supplies), for things like disableDeviceFallback and cancelLabel.

Face ID needs a usage string

Face ID ends the app the first time it is asked for without one. Add to Info.plist:

<key>NSFaceIDUsageDescription</key>
<string>Allow this app to use Face ID</string>

The module's config plugin writes this automatically. Android's USE_BIOMETRIC and USE_FINGERPRINT permissions are added automatically too - there is no separate ask-at-runtime permission dialog on either platform; authenticate() itself shows the system UI.

Without the module

authenticate() fails rather than passes without the module - { success: false, error: 'not_available' } - unlike every other service here, which falls back to reporting nothing. A lock that opens when its sensor is missing is not a lock. available() resolves to false and kinds() to an empty list.

Reference