Angular Guard失效

我希望我的身份验证卫士基于定期触发布尔值的可观察对象来允许/限制访问。我的想法是:

auth$ = interval(5000).pipe(map((n) => n % 2 === 0));

canActivate(
    next: ActivatedRouteSnapshot,
    state: RouterStateSnapshot
): Observable<boolean> | Promise<boolean> | boolean {
    return this.auth$;
}

It works when the triggers goes from false to true, but not the opposite, looks like the guard is not active anymore then.