In our project we have very complex security restrictions. When some Start event happens we grant some permissions to a set of sids. But when the corresponding End event happens we should revoke exactly the same set of permissions. It would be great if we can pass some optional key attribute to MutableAcl::insertAce method. In this case when the corresponding End event happens we can just remove all aces by passed key. This change can be made fully backward compatible. Will you accept PR from me with this change?