<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def create_refresh_token(self, access_token_value):
 # type: (str) -> str """ Creates an refresh token bound to the specified access token. """

        if access_token_value not in self.access_tokens:
            raise InvalidAccessToken('{} unknown'.format(access_token_value))

        if not self.refresh_token_lifetime:
            logger.debug('no refresh token issued for for access_token=%s', access_token_value)
            return None

        refresh_token = rand_str()
        authz_info = {'access_token': access_token_value, 'exp': int(time.time()) + self.refresh_token_lifetime}
        self.refresh_tokens[refresh_token] = authz_info

        logger.debug('issued refresh_token=%s expiring=%d for access_token=%s', refresh_token, authz_info['exp'],
                     access_token_value)
        return refresh_token