Refactor middleware for better readability

**Problem**
When working with config, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

The issue does not name files, tests, or a middleware entry point. Start by locating the middleware code that handles config and review its current error paths; done means the middleware is more readable and its config errors are more descriptive.

Written by the indexing model from the issue text.