The MQTT v3 spec has been updated to v3.1. The significant change is the inclusion of the option to send a username and password as part of the connect command. The new spec is available at and is a lot more readable and clear than the original. Mosquitto will support the v3.1 spec in a future release, along with the ability to control both broker and topic access by username. In the meantime, if you need this functionality, the IBM proprietary [RSMB] broker may be suitable for testing purposes. The RSMB package now also includes an MQTT client library, a simple publish client and a simple subscribe client, just like mosquitto. Be sure to check the license terms before using it! [RSMB]: http://www.alphaworks.ibm.com/tech/rsmb