Discussion: AuthBuilder still necessary?
Does AuthBuilder even need to be a widget anymore?
It looks like it's relying on widget lifecycle methods, but it may not need to. It also looks like the majority of these methods can be private members too. You may not even need auth builder anymore since it appears that it's only submitting the clipboard code.
One option is to delete AuthBuilder, make a little AuthCodeClipboard service and hook that up to the bloc.
I have no opinion either way.