code: func (a *PromptingAuthLoader) LoadAuth(path string) (*clientauth.Info, error) {
  	var auth clientauth.Info
  	// Prompt for user/pass and write a file if none exists.
  	if _, err := os.Stat(path); os.IsNotExist(err) {
  		auth = *a.Prompt()
  		data, err := json.Marshal(auth)
  		if err != nil {
  			return &auth, err
  		}
  		err = ioutil.WriteFile(path, data, 0600)
  		return &auth, err
  	}
  	authPtr, err := clientauth.LoadFromFile(path)
  	if err != nil {
  		return nil, err
  	}
  	return authPtr, nil
  }
docs: // LoadAuth parses an AuthInfo object from a file path. It prompts user and creates file if it doesn't exist.