Javadoc
Permission factory that delegates to another factory, and caches returned instances keyed by permission string
representation into weak map. The trick is, that permissions themself may be considered "static". The application
defines them upfront, and they are constant during runtime. The mapping of users to permissions (using different
concepts like "roles" or "groups") are volatile, but this factory has nothing to do with mapping, and even then, the
mapped permissions are still constants.