Add unit tests for controllers

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

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

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

Start by locating the controllers, middleware handling, configuration definitions, and existing unit tests in the repository. Read how middleware is currently selected or applied, then verify that an `enable_filtering` option defaults to `false` and that the intended filtering behavior is covered by controller tests.

Written by the indexing model from the issue text.