Ref T4712. Thus far, it seems that most "non-standard" things can be done pretty easily in the controller. Aside from deploying, this diff had to fix a few bugs / missing implementations of stuff.
(Notably, PhabricatorAuthProviderConfig, HeraldRule, PhabricatorSlowvotePoll, and AlmanacNetwork needed to implement PhabricatorApplicationTransactionInterface, PhabricatorAuthAuthProviderPHIDType had to be added, and a rendering bug in transactions of type PhabricatorOAuth2AuthProvider had to be fixed.)