Непосредственно из Firebase Doc
let user = Auth.auth().currentUser
if let user = user {
// The user's ID, unique to the Firebase project.
// Do NOT use this value to authenticate with your backend server,
// if you have one. Use getTokenWithCompletion:completion: instead.
let uid = user.uid
let email = user.email
let photoURL = user.photoURL
// ...
} else { // this else is not from doc
// no user is connected / signed in / logged in.
}