Microsoft To-Do (or outlook tasks) Graph Subscriptions

Is it possible to create a subscription for to-do tasks using the graph API (or through the outlook/365 APIs)?  Is there any way to get a "callback/webhook" type subscription for changes to a "task" in office 365?  It is a critical need for building integrations with the to-do application.  Anyone ever have a run at this, what did you come up with?  Thanks very much in advance.