JWT Tokens Demystified — Decoding the Three-Part String
Anatomy of a JWT, signing algorithms, access vs refresh tokens, and how to decode and verify them
You've seen them. Those impossibly long strings that start with eyJ and contain two dots. They show up in Authorization headers, cookies, and OAuth responses. They're JWTs — JSON Web Tokens — and they're the currency of modern authentication.
Your AI agent generates code that creates, validates, and stores JWTs. But JWTs have a reputation for being misused, and for good reason. They're deceptively simple on the surface and surprisingly easy to get wrong underneath. Let's crack one open and understand exactly what's inside.
What Is a JWT?
A JWT is a compact, URL-safe way to represent claims between two parties. In plain English: it's a small package of data that's been signed so you can verify it hasn't been tampered with.
The key insight is that a JWT is **not encrypted by defau
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