But in reality, it was a nightmare.

Even when it was just the Fingerprint API, there weren’t so many problems.

The guys from Google suggested a fantastic initiative and made a pretty good androidx.biometric library. However, it only added a layer of backward compatibility, and it did not solve the huge list of problems associated with biometrics.

Just a few examples from real life:

• On Android 9, there is no option to check biometric hardware, as well as biometric data registered in the system
• It is not clear how to define an in-display fingerprint scanner
• There are many devices with face unlocking, but BiometricPrompt does not have access to this functionality
• There is no way to choose or even to determine the type of biometric on the device
• OnePlus 6T: Fingerprint scanner does not recognize finger in the app
• OnePlus 6T: no BiometricPrompt UI for in-display scanner
• Face unlock stops working on Pixel 4 running Android 12 if the camera is “muted” from Quick Settings

I have been working on biometric authentication since the Samsung Pass release in 2014 and have some specific requirements for this procedure. Something like described in the code listed below:

Several key points:

• Ability to check biometric state BEFORE BiometricAuth started
• Compatibility with the most devices
• Consistent UI/UX across all OS versions and devices
• Face/IrisId unlock support, additionally to Fingerprint
• Blocking UI behind Biometric dialog (especially useful for dual-screen devices like Microsoft Surface Duo or LG Wing)
• Informing the user about biometrics used for authentification
• Plus, the issues mentioned above should be fixed

To meet these requirements, while also addressing known issues and limitations, I developed the complex of solutions, which were evolved into a separate library.

This is how the Advanced BiometricPromptCompat was born.

So, what BiometricPromptCompat library can do:

1) Fingerprint/BiometricPrompt auth of course

2) FaceAuth on Samsung, Xiaomi, Huawei, etc., vary from vendor and OS version

3) Iris Auth — Samsung devices

4) Compatible with Android OS versions starting from Android 4.1 and up to Android 12L and newer

5) BiometricManagerCompat allows checking the availability of biometric hardware, enrollments, sensor lockout, etc.

6) Allows to pick specific biometrics — for example, only Face or only Fingerprint

7) Determination of an in-display scanner

8) Fixes for devices with an in-display scanner without UI

9) Fixes for the “muted” camera on Android 12, that blocks FaceUnlock

For more features and compatible devices — see the “Key features” section.

To test the app please follow this link.

App test example on Huawei P40:

In general, the BiometricPromptCompat is made as similar as possible to the original BiometricPrompt and requires minimal changes in existing code.

Let’s look closer.

BiometricAuthRequest:

Allows configuring biometrics recognition behavior. The default is

BiometricAuthRequest (BiometricApi.AUTO, BiometricType.BIOMETRIC_ANY, BiometricConfirmation.ANY)

• BiometricApi is a way to work with biometrics sensors. It can be AUTO, BIOMETRIC_PROMPT, or LEGACY
• BiometricType specifies which biometrics to use. It can be BIOMETRIC_FINGERPRINT, BIOMETRIC_FACE, BIOMETRIC_IRIS
• BiometricConfirmation indicates the identity confirmation rule. If we specify ANY, any (if there are several) biometrics ends the authentication procedure. ALL will wait for all biometrics to verify their identity

BiometricManagerCompat

fun hasEnrolled (BiometricAuthRequest): Boolean

determines if biometric is registered on the device

fun isHardwareDetected (BiometricAuthRequest): Boolean

returns TRUE if the specified biometrics is available on the device

fun isLockOut (BiometricAuthRequest): Boolean

and

fun isBiometricSensorPermanentlyLocked (BiometricAuthRequest): Boolean

allows checking if biometrics are locked (short term or long term, respectively).

BiometricPromptCompat

Firstly, this is the main entry point to the library, so it is better to start initialization in the Application.onCreate(), just call

BiometricPromptCompat.init ()

After initialization is finished, we can start working with BiometricPromptCompat API

fun getAvailableAuthRequests: List <BiometricAuthRequest>

it returns the list of available biometrics on this device.

To work with biometric authentication flow, we need a BiometricPromptCompate instance. You need to use the builder for this:

val prompt = BiometricPromptCompat.Builder(BiometricAuthRequest, fragmentActivity).apply {
            this.setTitle(title)
            this.setNegativeButton("Cancel", null)
        }.build()

Now we are ready to start biometric authentication:

fun authenticate(BiometricPromptCompat.AuthenticationCallback)

And to cancel the biometric authentication dialog:

fun cancelAuthenticate()

For more detailed information, see the library documentation.