In intelligent vehicular networks, vehicles have enhanced sensing capabilities and carry computing and communication platforms to enable new versatile systems known as Vehicular Communication (VC) systems. Vehicles communicate with other vehicles and with nearby fixed equipment to support different applications, including those which increase driver awareness of the surroundings. This should result in improved safety and may optimize traffic. However, VC systems are vulnerable to cyber attacks involving message manipulation. Research aimed at tackling this problem has resulted in the proposal of multiple authentication protocols. Several existing survey papers have attempted to classify some of these protocols based on a limited set of characteristics. However, to date there is no generic framework to support the comparison of these protocols and provide guidance for design and evaluation. Most existing classifications either use computation complexity of cryptographic techniques as a criterion, or they fail to make connections between different important aspects of authentication. This paper provides such a framework, proposing a new taxonomy to enable a consistent means of classifying authentication schemes based upon seven main criteria. The main contribution of this study is a framework to enable protocol designers and investigators to adequately compare and select authentication schemes when deciding on particular protocols to implement in an application. Our framework can be applied in design, making choices appropriate for the intended context in both intra-vehicle and inter-vehicle communications. We demonstrate the application of our framework using two different types of case study: individual analysis and hypothetical design. Additionally, this work makes several related contributions. We present the network model, outline the applications, list the communication patterns and the underlying standards, and discuss the necessity of using cryptography and key management in VC systems. We also review the threats, authentication, and privacy requirements in vehicular networks.