JWT: Generating, Signing, and Verifying Tokens
Understand the structure and purpose of JWTs in authentication, including how to securely generate signed tokens and verify them on requests. Learn essential security rules for payload content and expiration to protect your MongoDB-backed MERN application.
The previous lesson verified a user's credentials at login, but that only proves identity for that one request. On the next request, the server has forgotten. A JSON Web Token (JWT) solves this: when login succeeds, the server issues a signed token the client sends back on later requests to prove who it is, with no session stored on the server. This lesson covers how tokens are structured, signed, and verified, and the two security rules that prevent the most common JWT mistakes.
Note: The examples use the
jsonwebtokenlibrary and are runnable. They sign and verify tokens with a secret; in production that secret lives in an environment variable, here it is shown inline for the demonstration.
To make the token concrete, the next visual should show its three parts and the sign-then-verify cycle.
That starts with what a token is made of.
The three parts of a JWT
A JWT is a single string with three parts separated by dots: header.payload.signature. Each part has a distinct role.
Header: ...