✅ JWT Introduction: JWT (JSON Web Token) is a compact, stateless token used for securely transmitting user identity between client and server. ✅ Compact & URL-safe: Small, Base64URL-encoded token ideal for headers & mobile apps. ✅ Stateless Auth: No server-side session storage; token itself carries all claims. ✅ Built-in Expiration: Uses exp, iat, nbf for time-based validity. ✅ Three Parts: Structured as header.payload.signature. ✅ Signed, Not Encrypted: Ensures integrity, not secrecy (HS256/RS2