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JSON Web Token (JWT)

  • Publish date
  • Category Web Development
  • Reading time 1 minutes and 5 seconds

JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object.

JWTs are most commonly used for Authentication and Authorization. Once a user logs in, the server issues a JWT. This token is signed (using a secret or a public/private key pair) so the server can verify that the “claims” inside it haven’t been tampered with. Because JWTs are stateless, the server does not need to store session data in memory, making them the preferred choice for scaling modern microservices and SPAs (Single Page Applications).

Frequently Asked Questions

For maximum security, JWTs should be stored in an HttpOnly, Secure cookie. Storing them in localStorage makes the token vulnerable to XSS attacks, as any malicious script can read the token and hijack the user’s account.

Yes. Standard JWTs are encoded (Base64Url), not encrypted. Anyone who intercepts the token can decode it to see the user’s ID or email. Therefore, you should never put sensitive data like passwords or credit card numbers inside the JWT payload.

Since JWTs are stateless, the server cannot “delete” a token once it is issued. Standard practice involves using short-lived Access Tokens and longer-lived Refresh Tokens. To force a logout, the server can “blacklist” the refresh token in a database like Redis.

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