code: public ApnsServiceBuilder withAuthProxy(Proxy proxy, String proxyUsername, String proxyPassword) {
          this.proxy = proxy;
          this.proxyUsername = proxyUsername;
          this.proxyPassword = proxyPassword;
          return this;
      }
docs: Specify the proxy and the authentication parameters to be used
  to establish the connections to Apple Servers.
  
  <p>Read the <a href="http://java.sun.com/javase/6/docs/technotes/guides/net/proxies.html">
  Java Networking and Proxies</a> guide to understand the
  proxies complexity.
  
  @param proxy the proxy object to be used to create connections
  @param proxyUsername a String object representing the username of the proxy server
  @param proxyPassword a String object representing the password of the proxy server
  @return  this