IssueTracker

When using any of the suspending extensions FragmentActivity.authenticateWithClassXBiometrics, failing to authenticate on the first try causes the method to throw an AuthPromptFailureException.
While this behavior is documented, it is highly undesireable, as the prompt window is still visible and allows the user to try again. In addition, trying to authenticate again will result in a IllegalStateException, because the underlying CoroutineAuthPromptCallback tries to resume its continuation twice.

BUILD INFO

• Device type: Oneplus 7T
• OS version: 11
• Biometric library version: 1.2.0-alpha03

STEPS TO REPRODUCE

1. enroll at least one fingerprint
2. invoke activity.authenticateWithClass2Biometrics("Authenticate", "Cancel")
3. attempt to authenticate with a fingerprint that has not been enrolled until you see an error message
4. authenticate with a fingerprint that has been enrolled

EXPECTED RESULTS
The suspend function should only complete or throw an exception when the prompt window reaches a terminal state

OBSERVED RESULTS
Unless caught, a IllegalStateException will crash your app

NUMBER OF TIMES YOU WERE ABLE TO REPRODUCE: 10/10, can reproduce again

Additional thoughts

I think this is rooted in a general misconception about when each method of BiometricPrompt.AuthenticationCallback is invoked. While the system invokes onAuthenticationFailed on valid but unrecognized attempts (see the android documentation), the of the androidx AuthPromptCallback wrapper, says "Called when an authentication attempt by the user has been rejected."

Proposed fix

In androidx.biometric.auth.CoroutineAuthPromptCallback, do not resume the continuation upon onAuthenticationFailed. Instead allow passing a (optional) lambda to to be invoked instead. This allows developers to handle the error, but does not force the suspend function to complete earlier than desired.