Improve error messages in auth

**Feature request**
It would be great to have notifications for core.

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

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

Start by locating the authentication configuration and the existing core notification handling. Trace how configuration options are defined and consumed, then verify that enable_notifications defaults to false and that enabling it provides the requested core notifications.

Written by the indexing model from the issue text.