This repository is the `express-jwt` npm package, a widely-used Express.js middleware for validating JSON Web Tokens (JWTs). The core function `expressjwt(options)` returns a middleware that extracts the JWT from the request (defaulting to the Authorization Bearer header), decodes it, verifies its signature using a provided secret or async callback, checks standard claims like audience and issuer, and optionally checks token revocation. The decoded payload is attached to `req.auth`. The middleware supports CORS preflight handling and integrates with `express-unless` for conditional skipping. It is a focused, well-structured library with clean TypeScript types and a simple architecture. The code is actively maintained by Auth0 with automated CI/CD for releases and testing across multiple Node.js versions. The primary reusable component is a generic deep property setter utility.