code: func AuthURL(authURL string) Option {
  	return func(c *CredHub) error {
  		if authURL != "" {
  			var err error
  			c.authURL, err = url.Parse(authURL)
  			return err
  		}
  		return nil
  	}
  }
docs: // AuthURL specifies the authentication server for the OAuth strategy.
  // If AuthURL provided, the AuthURL will be fetched from /info.