title: How to implement different authentication strategies in an Express app, without using Passport.js?
body: <p>My situation demands to implement an authentication mechanism in my express app (my stack is MERN) without using any 3rd party middleware for authentication (like passport.js). I have to implement many authentication strategies like Google, Facebook, local login, etc. What should be the folder/project structure and how to do it correctly for it to be scalable if more strategies come up later?</p>