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ok, I did some more research, turns out that callback notification goes to the if we press "cancel" button but goes wrong when authentication succeeds

as you can see in the attached project
if you open the bio-prompt in the 1st Fragment and authenticate
and after that you go to the 2nd Fragment and authenticate in the bio-prompt
callback notifies the Fragment1 instead of the Fragment2 as you can see in the logs

expected result is that Fragment2 is notified instead of Fragment1

also if you first go to Fragment2 and after that you go to Fragment1 always opening the prompt and doing the authentication
Fragment2 is notified instead of Fragment1

funny thing is that doing cancel instead of authentication notification works ok

https://drive.google.com/open?id=1ZVhp9sFBJ6pa1bKzHg1AM5tF5XnmyFMM

manually closing the FingerprintHelperFragment works as a workaround
```
   override fun onPause() {
        // WORKAROUND for https://issuetracker.google.com/issues/123857949
        activity?.let { activity ->
            activity.supportFragmentManager.findFragmentByTag("FingerprintHelperFragment")?.let {
                activity.supportFragmentManager.beginTransaction().remove(it).commitAllowingStateLoss()
            }
            super.onPause()
        }
    }
```

Issue is reproducible. More details are here - https://drive.google.com/corp/drive/folders/1jaiApoKzTxQc-Rg46D8qmP9MpKhkBo2D  (internal only link).

My mistake in point one:
1. Biometric#mLifecycleObserver#onResume should call mFingerprintHelperFragment.setCallback(...) even if mFingerprintDialogFragment is null.

Here is my temporary fix. Just place it in androidx.biometric package and use it like BiometricPrompt:

package androidx.biometric

import android.annotation.SuppressLint
import androidx.fragment.app.FragmentActivity
import java.util.concurrent.Executor

/**
 * Fix for isssue https://issuetracker.google.com/issues/123857949
 */
@SuppressLint("RestrictedApi")
class FixedBiometricPrompt(
    private val fragmentActivity: FragmentActivity,
    executor: Executor,
    callback: BiometricPrompt.AuthenticationCallback
) {
    private val delegate: BiometricPrompt

    init {
        // set executor and callback to helper fragment
        (fragmentActivity.supportFragmentManager.findFragmentByTag("FingerprintHelperFragment") as? FingerprintHelperFragment)?.setCallback(
            executor,
            callback
        )

        delegate = BiometricPrompt(fragmentActivity, executor, callback)
    }

    fun authenticate(info: BiometricPrompt.PromptInfo, crypto: BiometricPrompt.CryptoObject) {
        delegate.authenticate(info, crypto)
    }

    fun authenticate(info: BiometricPrompt.PromptInfo) {
        delegate.authenticate(info)
    }

    fun cancelAuthentication() {
        delegate.cancelAuthentication()
    }

    fun cleanup() {
        // remove executor and callback from helper fragment to prevent memory leak
        (fragmentActivity.supportFragmentManager.findFragmentByTag("FingerprintHelperFragment") as? FingerprintHelperFragment)?.setCallback(
            null,
            null
        )
    }
}