[@nativescript/biometrics] Issue with verifyBiometric on iOS 18.3.1: Unable to Retrieve Stored Secret When Using pinFallback

[kyrstencarlson]

Description

While using iOS 18.3.1, I encountered an issue with the verifyBiometric function where enabling pinFallback prevents retrieval of the stored secret.

Code Example

this._BiometricAuth.verifyBiometric({
    title: 'Authenticate',
    message: 'Verify your identity to access your account.',
    keyName: 'MyKeyName',
    pinFallback: true, // Allow fallback to device passcode
    ios: {
      fetchSecret: true, // Retrieve stored secret upon successful authentication
      customFallback: false, // Do not use custom fallback logic
    },
});

Expected Behavior

• If Face ID fails, the system should prompt the user to enter their device passcode.
• After successful authentication (via Face ID or passcode), the stored secret should be retrievable.

Actual Behavior

• When pinFallback: true, the stored secret is not accessible.
• This behavior seems to be affected by customFallback: false, even though I intend for it to behave similarly to Face ID authentication.
• If pinFallback: false, Face ID failures result in an error (SecItemCopyMatching), and the passcode prompt does not appear.

Question

Is there a way to retrieve the stored secret when pinFallback: true and customFallback: false? Am I missing a configuration that allows proper fallback behavior while still being able to fetch the stored secret?

Environment

• iOS Version: 18.3.1
• Biometric Authentication Library: @nativescript/biometrics: "1.3.1"
• Device Model: iPhone 15 Pro, iPhone 16

Any guidance or workarounds would be greatly appreciated!

[jcassidyav]

As noted here, enabling pin fallback disables the encryption functionality. this is because the underlying key used with the encryption is always protected by biometrics.