FromRequestParts<T> class abstract interface

Builds a T from a request, or rejects it.

Custom extractors implement this and are named at the call site with @Extract(MyExtractor). Configuration goes in the constructor, and a preconfigured variant is a subclass with a zero-argument const constructor, which is what the generated code calls.

final class BearerAuth implements FromRequestParts<AuthUser> {
  const BearerAuth({this.scope});

  final String? scope;

  @override
  Future<Result<AuthUser, Rejection>> extract(Request request) async { ... }
}

final class TodosWrite extends BearerAuth {
  const TodosWrite() : super(scope: 'todos:write');
}