LoginView.swift

SignInWithAppleButton(
    // Request User FullName and Email
    onRequest: { request in
        // You can change them if needed.
        request.requestedScopes = [.fullName, .email]
    },
    // Once user complete, get result
    onCompletion: { result in
        // Switch result
        switch result {
            // Auth Success
            case .success(let authResults):

            switch authResults.credential {
                case let appleIDCredential as ASAuthorizationAppleIDCredential:
                    let userID = appleIDCredential.user
                    if let firstName = appleIDCredential.fullName?.givenName,
                        let lastName = appleIDCredential.fullName?.familyName,
                        let email = appleIDCredential.email{
                        // For New user to signup, and
                        // save the 3 records to CloudKit
                        let record = CKRecord(recordType: "UsersData", recordID: CKRecord.ID(recordName: userID))
                        record["email"] = email
                        record["firstName"] = firstName
                        record["lastName"] = lastName
                        // Save to local
                        UserDefaults.standard.set(email, forKey: "email")
                        UserDefaults.standard.set(firstName, forKey: "firstName")
                        UserDefaults.standard.set(lastName, forKey: "lastName")
                        let publicDatabase = CKContainer.default().publicCloudDatabase
                        publicDatabase.save(record) { (_, _) in
                            UserDefaults.standard.set(record.recordID.recordName, forKey: "userID")
                        }
                        // Change login state
                        self.login = true
                    } else {
                        // For returning user to signin,
                        // fetch the saved records from Cloudkit
                        let publicDatabase = CKContainer.default().publicCloudDatabase
                        publicDatabase.fetch(withRecordID: CKRecord.ID(recordName: userID)) { (record, error) in
                            if let fetchedInfo = record {
                                let email = fetchedInfo["email"] as? String
                                let firstName = fetchedInfo["firstName"] as? String
                                let lastName = fetchedInfo["lastName"] as? String
                                // Save to local
                                UserDefaults.standard.set(userID, forKey: "userID")
                                UserDefaults.standard.set(email, forKey: "email")
                                UserDefaults.standard.set(firstName, forKey: "firstName")
                                UserDefaults.standard.set(lastName, forKey: "lastName")
                                // Change login state
                                self.login = true
                            }
                        }
                    }

                // default break (don't remove)
                default:
                    break
                }
            case .failure(let error):
                print("failure", error)
        }
    }
)
.signInWithAppleButtonStyle(.white) // Button Style
.frame(width:350,height:50)         // Set Button Size (Read iOS 14 beta 7 release note)