Add unit tests for services

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

**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 services and authentication configuration referenced by the issue, then find the existing unit-test structure for services. Clarify what auth requests or users should be filtered and how enable_filtering=false should behave; done means the option is covered by tests and filtering behavior is unambiguous.

Written by the indexing model from the issue text.