JWT Authentication Explained: How Stateless Tokens Replace Server Sessions

JWT (JSON Web Token) is a compact, signed token used in backend authentication to verify users without storing session data on the server. When a user logs in with credentials, the server generates a JWT comprising three parts — a header, a payload, and a cryptographic signature — and returns it to the client. The client then includes this token in every subsequent request, allowing the server to verify identity by checking the signature rather than querying a session store. Although the payload is Base64-encoded and readable by anyone, the signature ensures the token cannot be tampered with, since altering any data invalidates the signature without the server's secret key. Security best practices recommend storing tokens in HttpOnly cookies or secure platform storage rather than localStorage, to guard against cross-site scripting attacks.