OAuth2 Introspection Plugin

I would like to show how to work with the OAuth2 plugin and understand how it works in detail. To do that I need a simple OAuth2 provider that can also make an introspection endpoint available. I’m trying to do that with a DEV account in Okta, but it’s turning out to be a bit difficult. Could you let me know a simple and easy way to get an OAuth2 provider to work?