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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 async def generate_refresh_token(self, request, user):
 """ Generate a refresh token for a given user. """

        refresh_token = await utils.call(self.config.generate_refresh_token())
        user_id = await self._get_user_id(user)
        await utils.call(
            self.store_refresh_token,
            user_id=user_id,
            refresh_token=refresh_token,
            request=request,
        )
        return refresh_token