Internet of Things (IoT) consists of a large number of connected objects that are communicating with each other. In order to support trusted communication between IoT objects, effective authentication procedures should be applied between the communicating entities. In this paper a survey of IoT authentication techniques, which are proposed in the literature, is presented. The survey aims to help other researchers in delving into the details of such techniques by going through their classification and comparison. The classification has been done based on the inherent features of these authentication technique such as being distributed vs. centralized, flat vs. hierarchical, and more others. A comparison between these techniques according to the used evaluation models and their security analysis is illustrated.