I believe it's best to have only one scene and create your screens from different components, attach and remove them from the main scene as your application flows.
So you may want to move the code from your main scene into a main component, or you can probably still keep it there and just present a separate auth component before allowing the main Scene's main contents to display. for example set your main group / container to visible = false until after the auth process succeeds, hope this may be of help!
Joe
aspiring