code: func (fl *Flags) Options() (auth.Options, error) {
  	opts := fl.defaults
  	opts.ServiceAccountJSONPath = fl.serviceAccountJSON
  	if fl.RegisterScopesFlag {
  		opts.Scopes = strings.Split(fl.scopes, " ")
  		sort.Strings(opts.Scopes)
  	}
  	return opts, nil
  }
docs: // Options return instance of auth.Options struct with values set accordingly to
  // parsed command line flags.