The rapid evolution of vehicles leads to future vehicular technologies which improve transportation systems. One prominent technology is platooning networks where a vehicle, called platoon head, leads to a group of vehicles. Platoons not only improve the vehicle driving experience and safety but also reduce traffic congestion. Despite all these benefits, the authentication of vehicles for platoon networks is a critical problem in order to share and get access control to other vehicles. Moreover, due to the platoon networks’ complexity and high dynamic formation, it requires an efficient and robust authentication mechanism between vehicles. In this paper, we propose a blockchain-based authentication protocol for platoons using the concept of the platoon as a service. Our approach not only proposes an efficient protocol that reduces the computation and communication for the authentication but also improves the security with the use of a distributed authentication (Auth-I) data ledger across the network and a token-based platoon authentication (Auth-II), which is suitable for practical implementations in areas with different traffic density.