Ask HN: Any tutorial that explains the secure way of doing user authentication?

So I am a beginner, working on my first project without any tutorials. One thing I am stuck on is how to do user authentication, most resources I have found till now explains how to use a particular lib for authenticating users, but my concept behind authentication is still kinda foggy. What I am looking for is an overview of what happens or needs to be done for user authentication in a language agnostic way.