code: def refresh(self):
          
          params = {
              'grant_type': 'refresh_token',
              'refresh_token': self.refresh_token
          }
          response = self._post('oauth', 'token', params=params)
          response = self._handle_response(response)
          blob = response.json()
          self.access_token = blob.get('access_token', None)
          self.refresh_token = blob.get('refresh_token', None)
          if not (self.access_token and self.refresh_token):
              raise build_api_error(response, blob)
          return blob
docs: Attempt to refresh the current access token / refresh token pair.
  
          If successful, the relevant attributes of this client will be updated
          automatically and the dict of token values and information given  by the
          Coinbase OAuth server will be returned to the caller.