In an amazing article on SitePoint, Christopher Pitt demonstrates how to create an async PHP server that can requests a fingerprint scan on the client side. He uses React Native, WebSocket, an async PHP server, PHP preprocessing, ... Really amazing stuff.

I’m going to describe the process of building custom multi-factor authentication for all transactions. I don’t want to do the usual (and boring on its own) SMS or push notification one-time-password stuff. I want to build a fingerprint scanner right into my phone. In this tutorial, we’re going to look at how to set up a simple iOS app using React Native. We will also set up an asynchronous HTTP server, with a web socket connection to the app. We will follow this up by adding fingerprint scanning capabilities to the app, and asking for these fingerprint scans from the HTTP server. Then we will build an endpoint through which GET requests can request a fingerprint scan and wait for one to occur.

https://www.sitepoint.com/scan-fingerprints-async-php-react-native/