The "post-PC" era is longing for the convergence of heterogeneous wireless communication technologies to enable seamless data connectivity. Wireless Technologies such as Wireless Local Area Networks (WLAN), Worldwide Interoperability for Microwave Access (WiMAX), Long Term Evolution (LTE) etc., attract new opportunities for collaborative and complementary usage. In the post-PC era more and more applications are emerging to benefit from the ubiquitous nature of the mobile devices. However, with the range of approaches that are used to validate the mobile devices in heterogeneous wireless networks, the need for a user friendly, flexible and reliable method to interconnect and utilize the different classes of wireless networks is becoming inevitable. In this paper, we present and analyze the different authentication mechanisms that are available for wireless networks and evaluate their advantages and limitations. We then propose an enhancement to the Coordinated Robust Authentication (CRA) protocol that can be encapsulated within the RADIUS protocol utilizing the advantages of public key infrastructure. We also present a security and cost evaluation on the proposed enhanced protocol.