In this video, I break down the authentication concepts every developer should master, because I keep seeing the same misconceptions again and again. I start by clearly separating authentication (who you are) from authorization (what you can do), and I also explain why 401 and 403 are not the same. I show the typical API request flow: authentication is the first gate, then authorization decides whether you can access a protected resource. After that, I go into password storage—something most tutorials skip. I walk you through the evolution from plain text (game over after one breach) to MD5/SHA1 (fast hashing is actually the enemy) to bcrypt (deliberately slow with a cost factor), and I also mention Argon2 as an even better modern option. I explain hashing vs encoding vs encryption with simple demos, and I highlight why base64 is not security. Finally, I cover real-world auth flows developers use: Basic Auth, Digest Auth, API keys, sessions (cookie + session id), and token-based auth with JWT. I also clear the confusion that JWT is not “authentication”—it’s a token format—and OAuth2 is an authorization framework, not authentication. The goal is to help you choose the right approach based on your system and threat model, not just copy-paste what’s trending.