Emerging technologies including smart perception devices, environment-control actuators, information and communication technologies and large computing resources are the main tools enabling smart agriculture. However, the use of wireless communication makes smart agriculture networks susceptible to various attacks. In this paper, we propose a novel architecture to enable periodic data collection from sensors to cloud using machine-to-machine communication. A robust, anonymous and unlinkable authentication scheme is developed for the proposed architecture. Three-party authentication between the cloud server, gateway and sensor nodes is facilitated by the scheme. The protocol uses session-specific pseudo-names and temporary passwords to achieve anonymity and unlinkability for both sensor nodes and gateways. The protocol also provides easy revocation for removing compromised sensor nodes and gateways. Further, formal and informal proofs are provided, and through performance analysis, it is demonstrated that the proposed protocol outperforms other schemes in terms of security features and performance metrics.