code: func (m *Manager) getPubKey(u *url.URL) (*os.File, error) {
  	switch u.Scheme {
  	case "":
  		return os.Open(u.Path)
  	case "http":
  		if !m.InsecureAllowHTTP {
  			return nil, fmt.Errorf("--insecure-allow-http required for http URLs")
  		}
  		fallthrough
  	case "https":
  		return downloadKey(u, m.InsecureSkipTLSCheck)
  	}
  
  	return nil, fmt.Errorf("only local files and http or https URLs supported")
  }
docs: // getPubKey retrieves a public key (if remote), and verifies it's a gpg key