I need a tutorial for custom integration with authentik

[CakeEaterGames]

Hello!
Here's a brief exlanation my problem. Our company has a bunch of microservices. All of them have their own authentification logic. We'd like to use Authentik (or some other solution) to create a SSO that would unify the auth logic across all services.
There is plenty of documentation on how to connect well known services to Authentik, but I can't seem to find any documentation on how to integrate my own apps with Authentik.
I don't even know where to start. Can you please give me some directions? Is there some kind of a sample project or a tutorial or an article or a YouTube video that would help me to get started?