For owncloud/client#5056
Users can configure arbitrary subfolders for syncing, therefore we should
always return it when asked for.
The sync client makes sure to not always ask for it to save bandwidth.
This fixes infinite loops that are caused whenever a user is about to solve a 2FA
challenge, but the provider app is disabled at the same time. Since the session
value usually indicates that the challenge needs to be solved before we grant access
we have to remove that value instead in this special case.
Class Throttler implements the bruteforce protection for security actions in
Nextcloud.
It is working by logging invalid login attempts to the database and slowing
down all login attempts from the same subnet. The max delay is 30 seconds and
the starting delay are 200 milliseconds. (after the first failed login)
