code: func JWTConfigFromJSON(jsonKey []byte, scope ...string) (*jwt.Config, error) {
  	var key struct {
  		Email      string `json:"client_email"`
  		PrivateKey string `json:"private_key"`
  	}
  	if err := json.Unmarshal(jsonKey, &key); err != nil {
  		return nil, err
  	}
  	return &jwt.Config{
  		Email:      key.Email,
  		PrivateKey: []byte(key.PrivateKey),
  		Scopes:     scope,
  		TokenURL:   JWTTokenURL,
  	}, nil
  }
docs: // JWTConfigFromJSON uses a Google Developers service account JSON key file to read
  // the credentials that authorize and authenticate the requests.
  // Create a service account on "Credentials" page under "APIs & Auth" for your
  // project at https://console.developers.google.com to download a JSON key file.