biometric authentication in my web app

Ok before saying this question is a copy please read my problem.

I want to create a web app, for example for a gym. and it will have following features.

1. admin (owner ) can check and control the attendnce and monthly fees of the customers.

2. Each customer will mark attendence biometricaly, i.e : fingerprints.

Note: There will be only one machine, means client and server will be the same machine/computer.

So please tell me how can I do this that customers mark their attendnce everyday through finger prints and it checks if the customer is new or existing ( obviously ) , and also keeps the record of all attendence by a specific customer.

I only need suggestion about the fingerprinting part,rest of the application I can develop.

I havent decided server side language yet because I dont know which must be required for this feature, but I am pretty good with ASP.NET CORE ( open source) and python.

So please tell me what are my options and what is the simplest way to do it. Thanks in advance