The text you are looking for likely refers to the Fundamentals of Backend Engineering course on Udemy by Hussein Nasser
Session-based auth stores data on the server (not portable). JWT (JSON Web Tokens) stores data in the token itself. A solid Udemy course will teach you how to issue and verify JWTs, meaning your auth logic works across millions of servers.
This is the definition of portable. When you finish the course, delete the container. No system clutter.
Backend engineering is fundamentally about moving bytes over a network. You cannot build a portable backend without mastering HTTP verbs (GET, POST, PUT, DELETE), status codes (404, 201, 500), and stateless architecture. Good Udemy courses will teach you how to design a REST API that any frontend (Web, iOS, Android) can consume.
But now, the plane hit turbulence. The screen flickered.