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)
* Add InvalidTokenException
* add DefaultTokenMapper and use it to check if a auth token exists
* create new token for the browser session if none exists
hash stored token; save user agent
* encrypt login password when creating the token
