OptionalloadLoads channel code on demand, given the ClientPluginClass keys of the channels a session could use. The
one-script element supplies it so a heavy channel (the Interactive Component channel's React runtime)
downloads only when it is in scope. Absent, every channel the page can name is already in the bundle.
Optionalnow
Builds the auth adapter for an api-url and (when the credential can be renewed) a renewer.