code: func JWTConfigFromJSON(jsonKey []byte, scope ...string) (*jwt.Config, error) {
  	var f credentialsFile
  	if err := json.Unmarshal(jsonKey, &f); err != nil {
  		return nil, err
  	}
  	if f.Type != serviceAccountKey {
  		return nil, fmt.Errorf("google: read JWT from JSON credentials: 'type' field is %q (expected %q)", f.Type, serviceAccountKey)
  	}
  	scope = append([]string(nil), scope...) // copy
  	return f.jwtConfig(scope), 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" for your project at
  // https://console.developers.google.com to download a JSON key file.