例如(取自 Realm 的文档):
let usernameCredential = Credential.usernamePassword(username: "username", password: "password", actions: [.createAccount])
let googleCredential = Credential.google(token: "Google token")
let facebookCredential = Credential.facebook(token: "Facebook token")
let iCloudCredential = Credential.iCloud(token: "iCloud token")
如何将这些帐户链接在一起,以便这些帐户中的任何一个连接到同一个领域?