[Zope] User groups

Hi all, Is there a product available that would enable me to make user groups in Zope and assign local roles to the group, rather than the individual users. I want to use this in a multi-party CMF portal. I want to create a group for each party (be that a company, organisation, whatever) and then assign user, reviewer, etc. local roles to the group instead of each user. I would be easy enough to write this so that the group object handles the individual user local role assignment and removal, but something a bit closer to the Zope security system would be preferable. Thanks Etienne