@Override
                    public void completed(final AsyncExecRuntime execRuntime) {
                        final HttpHost proxy = route.getProxyHost();
                        tracker.connectProxy(proxy, route.isSecure() && !route.isTunnelled());
                        if (LOG.isDebugEnabled()) {
                            LOG.debug("{} connected to proxy", exchangeId);
                        }
                        proceedToNextHop(state, request, entityProducer, scope, chain, asyncExecCallback);
                    }
Request execution handler in the asynchronous request execution chain
that is responsible for establishing connection to the target
origin server as specified by the current connection route.

@since 5.0
httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/AsyncConnectExec.java