E aí, pessoal! Lucas here from São Paulo.
When implementing user logins in modern web apps, JSON Web Tokens (JWT) are the industry standard. But I see a lot of developers using libraries to handle JWTs without understanding what they actually are.
The Three Parts of a JWT
If you look at a JWT, it’s just three random-looking strings separated by dots: `header.payload.signature`.The biggest misconception is that JWTs are encrypted. They are NOT. The header and payload are simply Base64 encoded. Anyone who intercepts the token can decode it and read your payload (which is why you should never put passwords or sensitive info inside them!).
The third part, the signature, is what makes it secure. It proves that the token was generated by your server and hasn't been tampered with.
Decoding Tokens for Debugging
When I'm debugging frontend authentication issues, I always use the local JWT Decoder tool. I paste in the token, and it instantly shows me the JSON payload so I can check if the user roles and expiration timestamps are correct. Since the tool runs entirely in the browser, my session tokens are never exposed to a third party.Understand your tools, and you'll write much better code!