How JWT Authentication Works and How to Use It Securely

A JSON Web Token (JWT) is a three-part string — header, payload, and signature — used to authenticate users in stateless applications without server-side session storage. When a user logs in, the server verifies their credentials, generates a signed JWT containing user data, and sends it back to the client for use in subsequent requests. Because the payload is only base64-encoded and not encrypted, sensitive information such as passwords should never be stored inside a token. Security best practices include storing tokens in httpOnly cookies rather than localStorage to reduce XSS risk, setting short expiration times, and preferring asymmetric RS256 signing over symmetric HS256 in production. JWTs are well-suited for stateless APIs, mobile apps, and single sign-on systems, but traditional server-side sessions may be preferable when instant token revocation is required.