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Improved Biometric Authentication Documentation #39

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marcprux merged 1 commit into from
Jul 18, 2026
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Improved Biometric Authentication Documentation #39

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19 changes: 16 additions & 3 deletions README.md
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Expand Up @@ -950,11 +950,24 @@ Use `allowsDeviceCredentialFallback: false` when your app presents its own passc

### Platform Notes

On iOS, `BiometricAuthentication` uses `LocalAuthentication.LAContext`. When `allowsDeviceCredentialFallback` is `true`, iOS uses `.deviceOwnerAuthentication`; otherwise it uses `.deviceOwnerAuthenticationWithBiometrics`. On Android, SkipKit uses AndroidX `BiometricPrompt` with strong biometric authenticators. When `allowsDeviceCredentialFallback` is `true`, Android uses `BIOMETRIC_STRONG | DEVICE_CREDENTIAL` and does not show a negative button, because AndroidX does not allow a negative button together with device credentials.
#### Darwin
* On iOS/iPadOS/macOS, SkipKit uses `LocalAuthentication.LAContext`.
* When `allowsDeviceCredentialFallback` is `true`, the system uses `.deviceOwnerAuthentication`; otherwise, it uses `.deviceOwnerAuthenticationWithBiometrics`.

### Android Permissions
iOS/iPadOS Apps using biometric authentication with Face ID must include `NSFaceIDUsageDescription` in their `Info.plist`:

```xml
<key>NSFaceIDUsageDescription</key>
<string>Use Face ID to securely unlock the app.</string>
```

If Face ID is requested without this usage description, iOS/iPadOS will terminate the app. Touch ID does not require a separate usage-description key.

#### Android
* On Android, SkipKit uses AndroidX `BiometricPrompt` with strong biometric authenticators.
* When `allowsDeviceCredentialFallback` is `true`, the system uses `BIOMETRIC_STRONG | DEVICE_CREDENTIAL`. In this mode, the prompt will not show a cancel button, because AndroidX does not allow a cancel button together with device credentials.

Android apps using biometric authentication must include the biometric permission in their manifest:
Android apps using biometric authentication must include the biometric permission in their `AndroidManifest.xml`:

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