code: def _token_endpoint_request(request, token_uri, body):
      
      body = urllib.parse.urlencode(body)
      headers = {
          'content-type': _URLENCODED_CONTENT_TYPE,
      }
  
      response = request(
          method='POST', url=token_uri, headers=headers, body=body)
  
      response_body = response.data.decode('utf-8')
  
      if response.status != http_client.OK:
          _handle_error_response(response_body)
  
      response_data = json.loads(response_body)
  
      return response_data
docs: Makes a request to the OAuth 2.0 authorization server's token endpoint.
  
      Args:
          request (google.auth.transport.Request): A callable used to make
              HTTP requests.
          token_uri (str): The OAuth 2.0 authorizations server's token endpoint
              URI.
          body (Mapping[str, str]): The parameters to send in the request body.
  
      Returns:
          Mapping[str, str]: The JSON-decoded response data.
  
      Raises:
          google.auth.exceptions.RefreshError: If the token endpoint returned
              an error.