Workflow Security Pack (WFSP) is a collection of activities and associated plumbing to enable key security scenarios in WF 4.*. WFSP activities blend with the rest of the WF to bring end-to-end integrated security into workflow solutions.
Please see following resources for additional details:
http://zamd.net/2010/02/23/introducing-workflow-security-pack/
http://zamd.net/2010/05/18/integrating-wif-with-wf-4-0-and-appfabric/
http://msdn.microsoft.com/en-us/magazine/gg598919.aspx
http://wf.codeplex.com/releases/view/48114