Overriding the ActiveStorage controllers to add authentication or customize behavior is a bit tedious because it requires either: using custom routes, which means losing the nice url helpers provided by active storage copy pasting the routes in the application routes.rb, which is not very DRY.

it should be normal for production apps to add authentication and authorization to their ActiveStorage controllers. Unfortunately, there are 2 possible ways to achieve it currently: Not drawing ActiveStorage routes and do everything by yourself Override/monkey patch ActiveStorage controllers None of them is ideal because in the end you can't benefit from Rails upgrades (bug fixes, etc) so the intention of this PR is to let people define a parent controller (inspired by Devise, maybe @carlosantoniodasilva can tell us his experience on this feature) so that people can add authentication and authorization in a single place and still benefit from the default controllers.