Access control for shared resources is a complex and challenging task, in particular if the access control policy should be able to cope with different kind of sharing and collaboration. The reason for this is that traditional access control system often depend on administrators to set up the foundations of the access control mechanism, in most cases users and their group memberships. The access control model presented in this paper approaches this problem by supporting two different kinds of groups, named groups and resource-based groups. Using the implementation of this model in our application allows to to support a wide variety of sharing and collaboration types between the application’s users.