Spring Webflux: WebClient dealing with Expect: 100-continue

Question

I'm fairly new to Spring Webflux and working with the WebClient. What I have is for example a POST-Request being performed something like this:

Mono<ResponseEntity<Resource>> dotResponse = this.webClient
            .method(HttpMethod.POST)
            .uri(new URI("https://test.com/something"))
            .headers(headers -> headers.addAll(requestHeaders))
            .body(BodyInserters.fromResource(resource))
            .exchange()
            .flatMap(response -> response.toEntity(Resource.class));

In reality the code is a bit more complex, but this example is sufficient as a demonstration for the fundamental problem. Anyway this does work and I get the desired result. Now since the resource can be quite big, I want to use an "Expect: 100-continue"-header.

The problem is, what I get now is an empty 100 response, without any clue on how to trigger the remaining request. I couldn't find anything on Google or Stack Overflow, on how to approach this.

I would be most grateful for any pointers.