extract method
Produces the value, or the rejection that stops the handler.
Implementation
@override
Future<Result<T, Rejection>> extract(Request request) async {
final carried = request.context[extensionKeyFor<T>()];
if (carried is T) return Ok(carried);
return Err(
Rejection.internal(
'no $T in the request; add fromExtractor(...) where these routes are '
'mounted',
),
);
}