isEmailLinkSignInAllowed() {
    // Get provided sign-in options for specified provider.
    const signInOptions = this.getSignInOptionsForProvider_(
        firebase.auth.EmailAuthProvider.PROVIDER_ID);

    return !!(signInOptions && signInOptions['signInMethod'] ===
              firebase.auth.EmailAuthProvider.EMAIL_LINK_SIGN_IN_METHOD);
  }
@return {boolean} Whether email link sign-in is allowed. Defaults to false.