JWT (JSON Web Tokens) have become a default choice for authentication and authorisation in modern systems. They are widely adopted because they are: Stateless Scalable Easy to integrate across services But in real-world environments, especially distributed systems, JWT often introduces subtle security risks that are not immediately visible. Most JWT implementations are cryptographically correct… but architecturally flawed. This post explains: How JWT actually works Where implementations go wrong Real-world failure scenarios How to design JWT usage securely 1. What JWT Really Is A JWT is a signed token , not an encrypted one. It guarantees: Integrity (data hasn’t been modified) Authenticity (issued by a trusted entity) It does not guarantee: Confidentiality Correct usage across systems Authorisation correctness 2. JWT Structure A JWT consists of three parts: HEADER.PAYLOAD.SIGNATURE Enter fullscreen mode Exit fullscreen mode Visual Breakdown Header Defines metadata like algorithm used for signing.…