Microsoft Teams seems to be experiencing a bug since this morning. A recent update seems to have caused a "Select a certificate" prompt to be displayed to Teams users before they can use the software. The issue shows up when the service tries to reach us-prod.asyncgw.teams.microsoft.com while signing into the service. The prompt displays to users even before they can log in to use the software.
Microsoft has acknowledged the bug and is tracking the issue under the 'TM261228' advisory, where the company said:
"We've determined a recent deployment, designed to improve service performance, is inadvertently causing impact. We're reverting the update while we monitor the affected environment to validate that it resolves the issue."
Microsoft Teams users in Brazil, Costa Rica, APAC, EMEA, and EU are reported to be receiving the errors. However, Microsoft says only those users served through the infrastructure in North America are affected. Some users have been able to use the service by restarting the Microsoft Teams client.
Update: Microsoft has tweeted that it has reverted the update that caused the issue and can confirm that the service is restored and functional.