private void sendHandshake(String username, String password, OutputStream outputStream) throws IOException { final ConnectionAPI.HandshakeRequest.Builder builder = ConnectionAPI.HandshakeRequest.newBuilder(); if (username != null) { builder.putCredentials("security-username", username); builder.putCredentials("security-password", password); } builder.setValueFormat(serializer.getID()); final Message authenticationRequest = Message.newBuilder().setHandshakeRequest(builder).build(); authenticationRequest.writeDelimitedTo(outputStream); }