Is it possible to use the fingerprint scanner in the application like this?

Question

Android

Usage scenario:
One-time event. A person puts a finger on the sensor at the start, a fingerprint is read. Then (ideally) the data is sent to another smartphone at the finish line, the participant puts a finger, confirming the end of the event. Not ideal - the same smartphone is transferred to the finish line.
I suppose that iPhones simply do not give such access, but maybe Samsung, Meizu or others?

Answer 1

You can make sure that the fingerprint pressed against the sensor matches the fingerprint added in the security settings. And that's it. If there are several fingerprints in the settings, you will not be able to check which one worked. And even more so, you will not be able to transfer the fingerprint key to another device.
If you dig into the sources, you may come across an undocumented . The onAuthenticationSucceeded callback receives an AuthenticationResult. In Marshmallow, it contains a getFingerprint() method that returns a Fingerprint, which in turn contains a getName() method that returns the name given to the fingerprint. In Nougat, AuthenticationResult also has a getUserId() method . But you need to understand that these methods may change or disappear after the update.
Checking showed that at least on emulators AuthenticationResult.getFingerprint() returns null. I'm too lazy to go deeper and find out the reason for this.

Answer 2

It's impossible.
Even if there were public APIs for this, by comparing only two fingerprints it is impossible to say 100% for sure whether this is one person or not. That is why the devices ask you to put your finger on the scanner several times - the accuracy is low, the surface is small.
Perhaps an "industrial" scanner will help you - like those that are in consulates for taking biometrics.