Hello! I'm not sure. I don't think we have any content on that, so I can't help tons, but can point you in the right direction, or at least started on the right path. Please check out the following
You'll likely need to pay for it, but it shows you how to authenticate using a swift app as a client, and the authentication is really done using firebase. I think this is normally what you want to do, use a server to authenticate and then your app only communicates via an api, and you don't store or authenticate locally. I'm not positive on this though/
Having said that, for any local authentication (including storage of such data), it seems like you want to use keychain. Below are a few examples that seem related. Make sure you vet them, of course, as I can't speak to their legitimacy, nor exactly when and how to use them; I'd use them only to get a familiarity for things, and to spawn other searches:
If others have any experience with this, please weigh in!