R1:25ae4c458dda

Protect file data with a one-time-token

Test Plan: currently untested work in progress

Reviewers: #blessed_reviewers, epriestley

Subscribers: rush898, aklapper, Korvin, epriestley

Projects: #wikimedia

Maniphest Tasks: T5685

Differential Revision: https://secure.phabricator.com/D10054