code: func client(path string) (*http.Client, error) {
  	if path == "" {
  		return google.DefaultClient(oauth2.NoContext, compute.ComputeScope)
  	}
  
  	key, err := ioutil.ReadFile(path)
  	if err != nil {
  		return nil, err
  	}
  
  	jwtConfig, err := google.JWTConfigFromJSON(key, compute.ComputeScope)
  	if err != nil {
  		return nil, err
  	}
  
  	return jwtConfig.Client(oauth2.NoContext), nil
  }
docs: // client returns an authenticated HTTP client for use with GCE.