getSignInSuccessWithAuthResultCallback() {
    return (
        /** @type {?Config.signInSuccessWithAuthResultCallback} */ (
        this.getCallbacks_()['signInSuccessWithAuthResult'] || null));
  }
@return {?Config.signInSuccessWithAuthResultCallback} The callback to
    invoke when the user signs in successfully. The Auth result is passed
    into the callback, which includes current user, credential to sign in
    to external Auth instance, additional user info and operation type.
    An optional second parameter, the redirect URL, is also returned if
    that value is set in storage. If it returns `true`, the widget will
    continue to redirect the page to `signInSuccessUrl`. Otherwise, the
    widget stops after it returns.