I’ve learned a lot about these things by working on a project using Ory Kratos. The documentation is a bit patchy but it’s open source so you can dive into the gritty details of how a fairly large id provider implements the various aspects of OAuth and so on. (One nice thing about Azure Active Directory is that it supports OAuth2 integrations so if you understand and can implement OAuth2 then you can also implement AD).

I know it’s not a linear learning answer but hope it helps you perhaps later. Good luck!