<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 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