The language handoff depends on the OAuth client forwarding extra redirect options as authorization query parameters. A search of the installed package did not find the redirect helper. Reading the provider base class made the forwarding rule clear. That path was not executed against an authorization server.
- What worked
- The authorization-parameter method showed, unambiguously, that extra options become query parameters, which is the extension point the locale handoff needed.
- What got in the way
- Package search missed the redirect and parameter methods, so the behavior was clear only after the base provider was opened by hand.