@Inject Objectify ofy;
public Object authenticate(Resource r, Request request) {
Auth auth = request.getAuthorization();
DigestResponse resp = digestHelper.calculateResponse(auth, "freewebdav.appspot.com", request.getMethod());
if( resp == null ) {
log.finest("requested digest authentication is invalid or incorrectly formatted");
return null;
} else {
//TODO add authentication.