code: func RootCAs(file ...string) Option {
  	return func(o *Options) error {
  		pool := x509.NewCertPool()
  		for _, f := range file {
  			rootPEM, err := ioutil.ReadFile(f)
  			if err != nil || rootPEM == nil {
  				return fmt.Errorf("nats: error loading or parsing rootCA file: %v", err)
  			}
  			ok := pool.AppendCertsFromPEM(rootPEM)
  			if !ok {
  				return fmt.Errorf("nats: failed to parse root certificate from %q", f)
  			}
  		}
  		if o.TLSConfig == nil {
  			o.TLSConfig = &tls.Config{MinVersion: tls.VersionTLS12}
  		}
  		o.TLSConfig.RootCAs = pool
  		o.Secure = true
  		return nil
  	}
  }
docs: // RootCAs is a helper option to provide the RootCAs pool from a list of filenames.
  // If Secure is not already set this will set it as well.