Today I learnt that Teams too has a User-Agent String, and it defaults to that of the default browser of the OS. In my case, macOS with Firefox as the default, it was using the User-Agent String of Firefox. I encountered this today morning when Teams refused to sign on to our environment via ADFS because it wasn’t doing forms based as it usually did Windows Integrated Authentication, and that was failing because I am not on a domain joined machine.
All of this happened due to a chain of events. At work enabled WIA SSO on ADFS for Safari and Firefox. At home my VPN client re-connected today morning, causing DNS resolutions to happen via the VPN DNS server than my home router, resulting in ADFS sign on for Teams going via the internal route to the ADFS server at work and since this was set to accept WIA now for Firefox it was defaulting to that instead of forms based authentication. The fix for this was to sort out my DNS troubles … so did that, and here we are! :) Good to know!