After you apply this update, the Skype for Business Server 2015 OAuth (Open Authorization) protocol for server-to-server authentication and authorization can be optionally switched by using PowerShell.
Move-CsUser -Identity "UserAccountName" -Target "RegistrarPool FQDN" – UseOAuth
In this example, the OAuth authentication method is invoked when you move the user account by using the Identity to the Registrar pool. Otherwise, the Skype for Business Server will use the existing legacy authentication.
How to get this update
To get this update, install the January 2019 cumulative update 6.0.9319.537 for Skype for Business Server 2015, Core Components.