code: public void saveTo(File propertyFile) throws IOException {
          Properties props = new Properties();
          props.put("username", username);
          props.put("key", accessKey);
          FileOutputStream out = new FileOutputStream(propertyFile);
          try {
              props.store(out, "Sauce OnDemand access credential");
          } finally {
              out.close();
          }
      }
docs: Persists this credential to the disk.
  @param propertyFile File object to save java propery style credentials to.
  @throws IOException If the file I/O fails.