Microsoft has shed some light on the root cause behind yesterday’s massive Azure authentication outage. Microsoft said the outage resulted from an Azure Active Directory (Azure AD) configuration issue. The issue prevented users from authenticating to Microsoft 365, Exchange Online, Microsoft Teams, Xbox Live, Intune, Outlook.com, Office Web, SharePoint Online, OneDrive for Business, Yammer, and more. Microsoft is still working on bringing back up Intune and Microsoft Managed Desktop, with the exception of Intune.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-explains-the-cause-of-yesterdays-massive-service-outage/