Azure Active Directory周りで障害らしい。

Authentication errors across multiple Microsoft or Azure services – Mitigated (Tracking ID SM79-F88)

Summary of Impact: Between approximately 21:25 UTC on Sep 28 2020 and 00:23 UTC on Sep 29 2020, a subset of customers in the Azure Public and Azure Government clouds may have encountered errors performing authentication operations for a number of Microsoft or Azure services, including access to the Azure Portals. Targeted communications will be sent to customers for any residual downstream service impact.
Preliminary Root Cause: A recent configuration change impacted a backend storage layer, which caused latency to authentication requests.
Mitigation: The configuration was rolled back to mitigate the issue.
Next Steps: Services that still experience residual impact will receive separate portal communications. A full Post Incident Report (PIR) will be published within the next 72 hours.

だそうです。
Microsoft 365（Office 365）関連でサインイン周りにも影響でてますね。バックエンドストレージレイヤーの最近の構成変更の影響で認証要求の遅延が発生したとか。

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