Microsoft have widespread outage on the Office 365 login/authentication servers this morning and it’s affecting multiple tenancies.

The official report from the Microsoft 365 Service health status page says:

“Current status: We’ve identified a network issue that is affecting authentication to multiple Microsoft 365 services. We’re moving services to alternate network links to resolve the issue while we perform targeted service restarts in parallel to provide more immediate relief.

Preliminary root cause: A portion of network infrastructure that facilitates authentication requests is degraded, affecting access to one or more Microsoft 365 services.

More info: Customers that have their authorization cached are unaffected by this issue, and new authentications are succeeded approximately 50 percent of the time.”

From my testing there is an issue with DNS for login.microsoftonline.com – this is an alias for an Akamai host which again is an alias for another different host. Some DNS lookups (all in my case) against this hostname return no data.