JWT Explained: What JSON Web Tokens Are and How They Work
A plain-English introduction to JWTs: the three-part structure, Base64URL encoding, and how tokens carry signed claims.
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Tags: security, jwt, authentication
JWT Explained: Structure, Claims, and How They Work JSON Web Tokens (JWTs) appear in authentication flows everywhere — browser local storage, Authorization headers, cookie values, OAuth responses. They look like random strings until you know the format. Once you understand the structure, you can decode any JWT in seconds and see exactly what information it carries. This guide explains the three-part structure, how base64url encoding works, what claims mean, and how to decode a JWT without any library. What Is a JWT? A JWT is a compact, self-contained token that carries claims — statements about a subject (typically a user) — in a format that can be verified by anyone who has the signing key. The key properties: Compact: Small enough to fit in a URL or HTTP header Self-contained: The token…
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