Build Production-Grade Node.js Express Middleware with Logging and Auth

Create configurable Express middleware with structured logging, custom error classes, performance metrics, and comprehensive tests.

📝 The Prompt

Write a production-grade Express.js middleware in [JAVASCRIPT_OR_TYPESCRIPT] that handles [MIDDLEWARE_PURPOSE] for a [APPLICATION_TYPE] application. **Core Behavior:** The middleware should intercept [REQUEST_TYPES] requests and perform the following: 1. [PRIMARY_ACTION] — describe the main logic (e.g., verify JWT tokens, transform request body, enforce rate limits) 2. Attach processed data to `req.[CUSTOM_PROPERTY]` for downstream route handlers 3. Call `next()` on success or `next(error)` on failure with appropriate HTTP status codes **Implementation Requirements:** 1. **Configuration**: Export a factory function that accepts an options object: `{ [CONFIG_PARAMS] }`. This allows different routes to use the middleware with different settings. 2. **Error Handling**: Create a custom error class `[ERROR_CLASS_NAME]` extending `Error` with `statusCode`, `code`, and `details` properties. Throw structured errors that a centralized error handler can process. 3. **Logging**: Integrate structured logging using [LOGGING_LIBRARY] (e.g., winston, pino). Log middleware entry, decision outcomes, and errors with correlation IDs from `req.headers['x-request-id']`. 4. **Performance**: Add timing metrics using `process.hrtime.bigint()` and log middleware execution duration. Skip processing for [EXCLUDED_ROUTES] using path matching. 5. **Testing**: Write 4 test cases using [TEST_FRAMEWORK]: successful pass-through, authentication failure, malformed input, and skipped route. Include the middleware file, the custom error class, and the test file. Add inline comments for non-obvious decisions.

💡 Tips for Better Results

Use the factory function pattern (middleware that returns middleware) — specify your config params clearly for the best result. Always include a custom error class to avoid losing error context in production. Request path-exclusion logic upfront so health-check and public routes aren't blocked.

🎯 Use Cases

Node.js backend engineers use this when building middleware layers for authentication, request validation, or request enrichment in Express-based APIs.

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