code: def _get_credentials(self):
          
          uri = URITemplate(self.baseuri + '/{username}/credentials').expand(
              username=self.username)
  
          resp = self.session.post(uri)
  
          self.handle_http_error(
              resp,
              custom_messages={
                  401: "Token is not authorized",
                  404: "Token does not have upload scope",
                  429: "Too many requests"})
          return resp
docs: Gets temporary S3 credentials to stage user-uploaded files