Fix Legalpad for logged-out users

Summary: Fixes T5739. I only got D9857 half right: the new method names are correct, but the bodies needed to change too.

Test Plan: Signed a document as an anonymous user.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T5739

Differential Revision: https://secure.phabricator.com/D10191