code: async def add_user(self, username, password=None, display_name=None):
          
          if not display_name:
              display_name = username
          user_facade = client.UserManagerFacade.from_connection(
              self.connection())
          users = [client.AddUser(display_name=display_name,
                                  username=username,
                                  password=password)]
          results = await user_facade.AddUser(users)
          secret_key = results.results[0].secret_key
          return await self.get_user(username, secret_key=secret_key)
docs: Add a user to this controller.
  
          :param str username: Username
          :param str password: Password
          :param str display_name: Display name
          :returns: A :class:`~juju.user.User` instance