Filtering with centralized stitching

[Arik-Shapiro]

Is it possible to use filtering when using centralized stitching?
https://github.com/ChilliCream/hotchocolate-examples/tree/master/misc/Stitching/centralized
In this example how would you add product filtering to the Stitching.graphql?

extend type Query {
  me: User! @delegate(schema: "accounts", path: "user(id: 1)")
  topProducts(first: Int = 5): [Product] @delegate(schema: "products")
  products: [Product] @delegate(schema: "products")
}

[PascalSenn]

Yo can add filtering to the downstream service and stitch it. But at the moment you cannot "add" filtering on the stitching layer

[Arik-Shapiro]

Thank you for your answer!
Just to clarify, In the example there's this code

extend type Product {
  reviews: [Review] @delegate(schema: "reviews" path:"reviewsByProduct(upc: $fields:upc)")
}

that delegates it to the function

        public IEnumerable<Review> GetReviewsByProduct(
            [Service] ReviewRepository repository,
            int upc) =>
            repository.GetReviewsByAuthorId(upc);

that means that in-order to stitch the reviews to the product I need a separate filtering function on ReviewsService?
can't I just use the regular GetReviews function with filtering?
something like this:

        [UseFiltering]
        public IEnumerable<Review> GetReviews(
            [Service] ReviewRepository repository) =>
            repository.GetReviews();


extend type Product {
  reviews: [Review] @delegate(schema: "reviews" path:"reviews(where: {upc: {eq: $fields:upc}})")
}

Sorry if this is a silly question.

edit:
it actually works with

extend type Product {
  reviews: [Review] @delegate(schema: "reviews" path:"reviews(where: {upc: {eq: 1}})")
}

but "$fields:upc" returns an error
"extensions": {
"message": "Unexpected token: $.",
...

[vickytr44]

Is there a way to pass $fields:upc to the where clause?