code: func (d *driver) URLFor(ctx context.Context, path string, options map[string]interface{}) (string, error) {
  	methodString := "GET"
  	method, ok := options["method"]
  	if ok {
  		methodString, ok = method.(string)
  		if !ok || (methodString != "GET") {
  			return "", storagedriver.ErrUnsupportedMethod{}
  		}
  	}
  
  	expiresTime := time.Now().Add(20 * time.Minute)
  
  	expires, ok := options["expiry"]
  	if ok {
  		et, ok := expires.(time.Time)
  		if ok {
  			expiresTime = et
  		}
  	}
  	logrus.Infof("methodString: %s, expiresTime: %v", methodString, expiresTime)
  	signedURL := d.Bucket.SignedURLWithMethod(methodString, d.ossPath(path), expiresTime, nil, nil)
  	logrus.Infof("signed URL: %s", signedURL)
  	return signedURL, nil
  }
docs: // URLFor returns a URL which may be used to retrieve the content stored at the given path.
  // May return an UnsupportedMethodErr in certain StorageDriver implementations.