[Feature Request] Skip unneeded confirmation button after successful authentication with face unlock

[victor-marino]

Is your feature request related to a problem? Please describe.

When using a phone with face unlock (e.g.: Pixel 8 or Pixel 9), the user is not automatically taken to the app after successful authentication. Instead, they're required to tap a "Confirm" button.

I can't take a screenshot of the biometric prompt, but here's an example from the Android docs:

The reason is that on Android, biometric prompts are created as "sensitive" by default unless specified otherwise. This is fine for high-risk operations, such as confirming a purchase, but it doesn't make sense for low-risk actions like logging into an app. To avoid this step and provide a smooth user experience, biometric prompts should be marked as non-sensitive.

Describe the solution you'd like

The fix is extremely simple.

In Flutter, all that needs to be done is pass the sensitiveTransaction: false flag when creating the biometric prompt in line 48 of initializeBiometrics.dart, as indicated in the local_auth docs:

if (authAvailable) {
  //bool biometricsOnly = (await auth.canCheckBiometrics);
  return (await auth.authenticate(
    localizedReason: "verify-identity".tr(),
-    options: AuthenticationOptions(biometricOnly: false),
+    options: AuthenticationOptions(biometricOnly: false, sensitiveTransaction: false),
  ))
      ? AuthResult.authenticated
      : AuthResult.unauthenticated;
}

Once this change is done the authentication flow will work as intended when using face unlock: the user will briefly see the face unlock indicator, then they will be taken straight to the app. I can confirm apps also "feel" much faster when this is implemented properly, even though this has nothing to do with the performance of the app itself :-)