getRecaptchaParameters() {
    let recaptchaParameters = null;
    this.getSignInOptions_().forEach(option => {
      if (option['provider'] == firebase.auth.PhoneAuthProvider.PROVIDER_ID &&
          goog.isObject(
              option['recaptchaParameters']) &&  // Confirm valid object.
          !Array.isArray(option['recaptchaParameters'])) {
        // Clone original object.
        recaptchaParameters = googObject.clone(option['recaptchaParameters']);
      }
    });
    if (recaptchaParameters) {
      // Keep track of all blacklisted keys passed by the developer.
      const blacklistedKeys = [];
      // Go over all blacklisted keys and remove them from the original object.
      BLACKLISTED_RECAPTCHA_KEYS.forEach(key => {
        if (typeof recaptchaParameters[key] !== 'undefined') {
          blacklistedKeys.push(key);
          delete recaptchaParameters[key];
        }
      });
      // Log a warning for invalid keys.
      // This will show on each call.
      if (blacklistedKeys.length) {
        log.warning(
            'The following provided "recaptchaParameters" keys are not ' +
            'allowed: ' + blacklistedKeys.join(', '));
      }
    }
    return recaptchaParameters;
  }
@return {?Object<string, *>} The filtered reCAPTCHA parameters used when
    phone auth provider is enabled. If none provided, null is returned.