def isRealmUser(self, realmname, username, environ):
        """Returns True if this username is valid for the realm, False otherwise."""
        try:
            course = self.course_factory.get_course(realmname)
            ok = self.user_manager.has_admin_rights_on_course(course, username=username)
            return ok
        except:
            return False
Returns True if this username is valid for the realm, False otherwise.