This repository is a simple example of how to use ASP.NET Core Identity without Entity Framework.
I created it to help answer this StackOverflow question back in the early days of ASP.NET Core.
It just uses an in-memory list to store the user data, so it's not intended for real-world use. It's just a simple example to show how the various parts fit together, so that you can use it for inspiration when building your own system.