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Middleware is the backbone of your web framework. It lets you handle repeated tasks in one pipeline. Good middleware makes your app secure and easy to maintain.
The pattern wraps a handler function. Each piece of middleware calls the next. Order is key. Put logging first. Put authentication before rate limiting.
Authentication:
- Extract credentials from headers.
- Validate them.
- Attach user identity to the request.
- Return 401 for invalid credentials.
- Keep authorization separate.
Logging:
- Capture request method and path.
- Track status codes and duration.
- Use a unique request ID.
- Use structured logs for easy search.
Rate Limiting:
- Check request counts.
- Return 429 when limits are hit.
- Use Redis for speed.
- Identify clients by IP or user ID.
Request Validation:
- Check payload structure.
- Check data types.
- Stop bad data from reaching business logic.
- Use Zod, Joi, or Pydantic.
Error Handling:
- Catch unhandled exceptions.
- Return consistent error responses.
- Hide stack traces in production.
- Give clients a request ID for reports.