Wireless Mesh Networks, WMNs, are foreseen to be an alternative to LANs and last- mile access infrastructures, and they have many unique characteristics, such as ease of deployment and installation, and cost efficiency. Security is crucial for WMNs to be widely accepted as internetworking and access network technologies. Access control, as a security requirement, is one of the most important pillars that lay down the foundation for such an acceptance. We identify in this paper the criteria that should be fulfilled by a viable security solution to control access to WMNs, and specify DUA, a security scheme, that allows for mutual authentication. DUA is based on the distribution of authentication key material over many nodes in such a way that any coalition of a predetermined threshold of corrupted nodes or fewer does not compromise the security of the system. Further, the key material is never handled by a single node. In addition, DUA provides for efficiency through the use of lightweight cryptographic operations.