code: def create_refresh_token(self, access_token_value):
          # type: (str) -> str
          
          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
docs: Creates an refresh token bound to the specified access token.