// create a OkHttpClient builder instance and configure it to use the proxy
OkHttpClient client = new OkHttpClient.Builder()
    .proxy(proxy)
    .authenticator(new Authenticator() {
        @Override
        public Request authenticate(Route route, Response response) throws IOException {
            // If the proxy requires authentication, provide the credentials
            String credential = Credentials.basic(proxyUsername, proxyPassword);
            return response.request().newBuilder()
                .header("Proxy-Authorization", credential)
                .build()
            }
        })
        .build();