Consider deprecating old controllers API

**Feature request**
It would be great to have encryption for config.

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

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

No files, tests, or entry points are named. Start by locating how configuration is loaded and used in production deployments, then determine the expected encrypted format and key handling before adding the enable_encryption option with a false default; done means config encryption works when enabled and existing behavior remains unchanged when disabled.

Written by the indexing model from the issue text.