getCredentialHelper() {
    // Always use none for non http or https environment.
    // This could change when we support other credential helpers. This is
    // unlikely though as smartlock also checks the domain and will not work in
    // such environments.
    if (!util.isHttpOrHttps()) {
      return Config.CredentialHelper.NONE;
    }
    const credentialHelper = this.config_.get('credentialHelper');

    // Make sure the credential helper is valid.
    for (let key in Config.CredentialHelper) {
      if (Config.CredentialHelper[key] === credentialHelper) {
        // Return valid flow.
        return Config.CredentialHelper[key];
      }
    }
    // Default to using none.
    return Config.CredentialHelper.NONE;
  }
@return {!Config.CredentialHelper} The credential helper to use.