Developers beware, Microsoft's domain shakeup is coming soon

If you don't pay attention, your lovely little Teams app will stop working

Time is running out for developers and administrators to prepare themselves for Microsoft's one domain to rule them all –

Microsoft told the world of its plans to unify its domains just under a year ago and is now reminding developers that it really is time to remove your head from the sand, especially if you're a developer of Teams apps. is due to go live in June 2024, and tenants running apps that haven't been updated will remain on According to Microsoft: "This change impacts embedded applications where an external web app is rendered inside Teams, Outlook or Microsoft 365."

Microsoft's stated goal is to use for "non-product experiences" such as marketing or support, while will handle authenticated, user-facing product experiences.

The company said: "Initially, only net-new services will be deployed on the domain. Existing workloads have a broader range of implications to consider and will transition at a slower pace."

However, that was almost a year ago, and those workloads will have to move at some point, hence the notification for Teams app developers.

While will not be going anywhere in June 2024 – Microsoft expects it and to run in parallel – the direction of travel is clear. In its instructions for x-frame/CSP header updates to allow for the new domains, Microsoft said: "To ensure the app keeps working across existing and future Microsoft 365 hosts, please ensure to allow '*'."

An update to the TeamsJS client library to version 2.19 or higher, which includes a dynamic list of trusted domains, is also needed.

Microsoft said: "The transition to will benefit users and developers across the Microsoft 365 ecosystem. We are excited to take the next steps toward bringing Teams, Outlook, and Microsoft 365 onto the unified domain, and extending those benefits to app developers as well."

All of this means that affected developers must pay close attention to Microsoft's plans. A reduction in the fragmentation of domains will be welcomed but could also necessitate trawling through legacy code to ensure calls are not being made to places that might go away in the not-too-distant future. ®

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