Microsoft 365 is experiencing a multi-factor authentication (MFA) outage that blocks users from accessing multiple Microsoft 365 services such as Office 365 and Azure. Microsoft is analyzing the authentication logs in an attempt to isolate the cause behind the Microsoft 365 authentication outage affecting users for the past two hours. Microsoft says that only the admin center is currently affected by this issue, but users from the U.S. affected the most. Microsoft 365 MVP Brian Reid advises admins to disable MFA for all users for duration of outage.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-365-authentication-outage-users-unable-to-login/