We currently have a way to trigger SUL3 flow via a query parameter usesul3=1 but we don't have the inverse (with the flag). The inverse would be to just ignore the query param but we don't want sending usesul3=0 to do anything suspicious/unexpected in cases like central autologin etc.
So we need to implement usesul3=0 and make it do the expected thing we need across the CentralAuth codebase.