public void handle(Callback[] callbacks) throws IOException, UnsupportedCallbackException {
List<Callback> toRespondTo = new LinkedList<Callback>();
String userName = null;
Credential credential = null;
// A single pass may be sufficient but by using a two pass approach the Callbackhandler will not
// fail if an unexpected order is encountered.
// First Pass - is to double check no unsupported callbacks and to retrieve