code: public synchronized byte[] firstToken() {
      if (saslClient != null && saslClient.hasInitialResponse()) {
        try {
          return saslClient.evaluateChallenge(new byte[0]);
        } catch (SaslException e) {
          throw Throwables.propagate(e);
        }
      } else {
        return new byte[0];
      }
    }
docs: Used to initiate SASL handshake with server.