Glossary

Middleware

Middleware is an intermediate handler that intercepts an HTTP request before it reaches the controller — or a response before it reaches the client. Middleware form a chain: each one can pass the request along, modify it, or immediately return a response.

Typical uses

Authentication and authorization — verify a token before executing an action
Rate limiting — restrict requests per IP
Logging — record request/response details
CORS — add headers for cross-origin requests
Response compression — gzip before sending

The chain-of-responsibility pattern

Each middleware implements one method: receive the request, do its job, pass it on. If a condition is not met — return a response and break the chain. This pattern is framework-agnostic and appears identically in PHP, Python (WSGI), Node.js (Express), and Go.