If workspace is team managed, users can add/remove participants.
        Any user with the manage workspace permission can add/remove
        participants and admins.

def update_roster(self, REQUEST=None):
        """
        If workspace is team managed, users can add/remove participants.
        Any user with the manage workspace permission can add/remove
        participants and admins.
        """
        CheckAuthenticator(self.request)
        PostOnly(self.request)
        form = self.request.form
        entries = form.get('entries', [])
        self.update_users(entries)
        api.portal.show_message(message=_(u'Roster updated.'),
                                request=self.request)
        return self.request.response.redirect(
            '%s/@@edit-roster' % self.context.absolute_url())