Background. Smart grid is a new technology that focuses on utilising renewable energyalongside the current infrastructure. It aims to contribute to a sustainable future by implementingIoT devices in the electrical grid to adjust electricity flow and increase energyefficiency. By combining the current infrastructure with information technology manysecurity questions arise. This paper focuses on the authentication of the IoT devicesconnected with the MQTT protocol.Objectives. The study aims to discover a preferable MQTT authentication methodadapted for Techinova’s infrastructure with their requirements in consideration.Methods. A literature review was performed to obtain fundamental authenticationmethods and to distinguish different security approaches. Experiments were executed ina test environment to gather detailed information to gain a deeper understanding anddiscover security vulnerabilities.Results. The results derive from three experiments comparing the selected authenticationoptions security flaws.Conclusions. The results suggests that implementing TLS contributes to a secure authenticationand communication between the IoT devices and the broker without delayingthe transmission. However, further research could obtain other relevant data eventuatingin different results.