@UnstableApi
    public FutureTransformingRequestPreparation<ResponseEntity<String>> asString() {
        return asEntity(ResponseAs.string());
    }
Converts the content of the {@link HttpResponse} into a {@link String}.
For example:
<pre>{@code
WebClient client = WebClient.of("https://api.example.com");
CompletableFuture<ResponseEntity<String>> response =
    client.prepare()
          .get("/v1/items/1")
          .asString()
          .execute();
}</pre>
core/src/main/java/com/linecorp/armeria/client/WebClientRequestPreparation.java