code: public static String getNonce(long issueTime) {
      long currentTime = new Date().getTime();
      return TimeUnit.MILLISECONDS.toSeconds(currentTime - issueTime) + ":" + Long.toString(System.nanoTime());
    }
docs: Returns a nonce value. The nonce value MUST be unique
  across all requests with the same MAC key identifier.
  
  @see <a href="https://tools.ietf.org/html/draft-hammer-oauth-v2-mac-token-05#section-3.1">3.1.
  The "Authorization" Request Header</a>
  
  @param issueTime the number of seconds since the credentials were issued to the client
  
  @return nonce value