Improve error messages in controllers

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

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

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

Start by reading the controller and configuration entry points related to auth and compare them with the issue title about error messages. Determine what “import for auth” means and where `enable_import` belongs; done should include the agreed behavior with the option defaulting to `false`, but the issue does not specify tests or a concrete implementation location.

Written by the indexing model from the issue text.