Active Support’s CurrentAttributes: a really useful but hated Rails feature?

Some people dislike ActiveSupport::CurrentAttributes, but it’s undeniably very convenient. It allows you to safely use the much-loved global variables within requests—a truly handy feature. I want to discuss why it might be disliked, touching on precautions and past security flaws, such as an instance where information leakage occurred with a Puma and Rails combination.