Social Authentication Class - Implementation class?

I am setting up access manager, on which I want to log in with external OAuth 2.0 IDP.

I found out, that I can log in with social media over OAuth, but there I am limited with identity providers.

Set-up was done while following this documentation:

When I want to choose "Other" from "Auth Provider" I have to specify Implementation class, but I can't find any documentation on how this class should look like - therefore I can not develop it since I don't know what it should include, where should it be placed and how to connect it with Social Authentication Class.

Could please anyone send me a link to a file from documentation of implementation class?

Best Regards

Sebastian Novak