Continuing on with my FAQ theme, Dave Wickert just directed me to a recently released security white paper for SSAS Tabular Models written by Cathy Dumas that I could not resist sharing with everyone.   The white paper describes the security model, roles and security considerations for handling credentials when connecting to a SSAS tabular model and connecting to a relational data source for processing.  There are examples of both static and dynamic security scenarios.  Dynamic security approaches shown include step-by-step instructions for creating models that implement security based on the currently logged on Windows user name or based on custom data passed to Analysis Services. Two different methods are used to apply row filters – one using many-to-many relationships in DAX, and one using a more computational approach are also covered.

The SSAS Tabular Model Security white paper is located at  http://msdn.microsoft.com/en-us/library/jj127437.aspx.