These are production users. We have checked these are legitimate users and their device is not jail broken as well. And after some several failures, strangely we got success for for some of them failed ones. We are trying to generate new keys only when it fails while calling "attestKey(:clientDataHash:completionHandler". So, What are the best practices we can follow in this case? We are using UserDefaults to save them right now which does not seem secure what's your thought on this?