public final HttpAsyncClientBuilder setProxy(final HttpHost proxy) {
        this.proxy = proxy;
        return this;
    }
Sets default proxy value.
<p>
Please note this value can be overridden by the {@link #setRoutePlanner(
  HttpRoutePlanner)} method.
</p>
@return this instance.
httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/HttpAsyncClientBuilder.java