The alternative title is "How to check the logged-in Realm user logged in via certain authentication provider?" OR "How to check a user is using a specific authentication provider/method?"
For an app start with an anonymous user and then linked to another authentication provider using user.linkUser(credentials: credential). Since the user always has a value either an anonymous user or a linked user.
How can I know if the current logged-in user is already linked with another auth provider e.g. "Sign in with Apple" or "Google"? This information needs to be known in order to hide the auth provider sign-in button.
In RealmSwift 10.12.0
There is an identifiers property under user. It is an array of RLMUserIdentity. the user identity contains a providerType string, https://docs.mongodb.com/realm-sdks/objc/latest/Classes/RLMUserIdentity.html#/c:objc(cs)RLMUserIdentity(py)providerType
Below is a sample output
print(">>> DEBUG:", user.identities.map { identity in (identity.identifier, identity.providerType)
[("611a27f9a1575af5ed15234e-lnnaeteekatdftrnsmpbpldr", "anon-user"), ("000766.23cbd125344c140b18ef0baa4deccaf32.61234", "oauth2-apple")]
Now you can check if the user identities contains the provider you care and hide the "sign in" button/link for that provider