[Microsoft Teams 4c7] Modern authentication failed here, but you

You may receive the above authentication error message when you are trying to login to your Microsoft Teams application from your corporate network with ADFS.

What is the cause of Microsoft Teams 4c7 error?

The reason for this issues is because Microsoft Teams requires Forms Authentication, when ADFS was deployed/setup the Forms Authentication wasn't enabled for the intranet usage (by default its disabled), it needs to be enabled explicitly.

How to resolve of Microsoft Teams 4c7 error?

1. Go to AD FS Microsoft Management Console
2. Go to Navigation Pane -> Authentication Policies.
3. Select Edit Global Primary Authentication from Actions in Details Pane.
4. Now on the Intranet tab select Forms Authentication.
5. Click OK and Apply changes.