Rapid convergence of heterogeneous wireless communication technologies such as Wireless Local Area Networks (WLAN), 4G: LTE/LTE-Advanced Mobile Broadband, 5G and Worldwide Interoperability for Microwave Access (WiMAX), attract new opportunities for ubiquitous connectivity enabling collaborative usage. Hence, it is predicted that the ever-increasing use of wireless Internet demands a significant increase in wireless broadband throughput. However, to maintain reliable and seamless connectivity wireless devices entail simultaneous multi-gateway connections. Therefore, emerging technologies should be capable of performing secure roaming between the diverse wireless networks. Nevertheless, vertical handover (roaming) and seamless connectivity involve overcoming not only the incompatibility issues between the different wireless technologies but also the incompatibility issues amongst the authentication mechanisms used in the various wireless networks. For seamless connectivity, wireless devices need to authenticate in a timely fashion with the different types of wireless networks. However, the authentication mechanisms used in these wireless networks can be specific and fitting only to those wireless technologies. Hence, roaming becomes a major challenge due to the incompatible authentication mechanisms, parameters and credentials. Further, users demand a single but unique set of credentials to authenticate the wireless devices in the heterogeneous wireless environment. In other words, future heterogeneous networks demand a coordinated authentication mechanism for vertical handover with the ability to use a single but unique set of credentials enabling secure and fast roaming.