Improve error messages in middleware

**Description**
Currently config lacks proper serialization support.

**Proposed solution**
Add configurable serialization with sensible defaults.

**Priority**: Low/Medium

Start by locating the middleware and configuration entry points in the repository, since no files or tests are named. Clarify whether the intended change is serialization support, improved error messages, or both; done should include configurable serialization with sensible defaults and the specified error behavior.

Written by the indexing model from the issue text.