We have been monitoring this incident for the last 24 hours and can confirm that this has been resolved.

A fix has been implemented and we are monitoring the results.

It has been identified that a critical Microsoft service outage has occurred, users using Microsoft Authentication will be unable to access their service.
Microsoft are aware of this and rolling back a change they made that caused the problem, you can track the status of this work at https://status.office.com/ or we will update here as soon as we have further information.