Refactor core for better readability

**Feature request**
It would be great to have filtering for controllers.

**Use case**
Many users need this functionality for production deployments.

**Implementation idea**
Add a new config option `enable_filtering` with default `false`.

No files, tests, or entry points are named. Start by locating controller handling and the configuration path for `enable_filtering`; done means controller filtering exists and the option defaults to `false`.

Written by the indexing model from the issue text.