Update auth documentation

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

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

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

No files, tests, or entry points are named. Start by locating the authentication configuration and its documentation, then determine what “search for config” should cover; done means documenting and implementing enable_search with a default of false and verifying the production-deployment use case.

Written by the indexing model from the issue text.