There have been widespread reports today from users being unable to log in to Microsoft services, including Office 365. While the company initially acknowledged only that the Azure Portal was down, it has since confirmed a "partial service interruption" affecting Azure Active Directory across multiple regions.
Most of those affected are in Europe - although it appears that some users across the EU have still been able to connect to services despite the AD issues. However, some users in Israel and South Africa have also reported problems with authentication via AD today.
On its Azure status page, Microsoft stated:
Starting at approximately 09:00 on 3rd Dec, 2015, customers began experiencing intermittent issues accessing Azure services that use, or have dependencies on Azure Active Directory. Engineering teams are actively investigating the root cause of the issue and are developing a mitigation strategy. A list of services reporting impact will be provided shortly. An update will be provided in 60 minutes, or as events warrant.
Azure Active Directory manages identity data for millions of customers around the world, and Microsoft has proudly touted uptime of over 99.99% in the past.
Update: The issues that were affecting Active Directory have apparently now been resolved, and Microsoft's Azure status page is reporting that "all services are working properly".
According to an earlier status update, "an Azure Active Directory configuration error [was] believed to be the root cause of the issue". Microsoft also acknowledged that "while impact was centralized to West Europe and North Europe, customers outside of these regions may have experienced issues as a result of configurations specific to their individual scenarios."