JSON Web Tokens (JWT): Structure and Validation
JWT explained: decode the header, payload, and signature. Understand claims, expiration, algorithm choices, and how to validate tokens safely.
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Tags: json, security, jwt
JSON Web Tokens (JWT) Explained: Structure, Claims, and Validation A JWT is three base64url-encoded JSON objects concatenated with dots. That is the entire physical format. Understanding what each part contains, what the signature actually proves, and what the signature does not protect is the difference between using JWTs correctly and introducing authentication vulnerabilities. What is the three parts: header, payload, signature? Take any JWT and split it on : Part 1 — Header (base64url-decoded): The field identifies the signing algorithm. is always . That is all the header contains in a standard token. Part 2 — Payload (base64url-decoded): The payload contains claims — statements about the subject. Some are standardized (registered claims), some are application-specific. Part 3 —…
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