Apple sign in causes FIRAuthErrorUserInfoNameKey=ERROR_EMAIL_ALREADY_IN_USE (Code = 17007) - firebase

Question

Using SwiftUI, Xcode12.5.1, Swift5.4.2, iOS14.7.1,
My Firebase-Email/Password Login-page shall be extended with other Login possibilities such as Apple-Login (eventually Google-login, Facebook-login etc).
My steps:
log in with Email/Password to Firebase
log out
log in with "Sign in with Apple"
--> Then I get the following error:
Error Domain=FIRAuthErrorDomain Code=17007
"The email address is already in use by another account."
UserInfo={NSLocalizedDescription=The email address is already in use by another account.,
FIRAuthErrorUserInfoNameKey=ERROR_EMAIL_ALREADY_IN_USE}
What I intended to do is to link the existing Email/Password-Firebase-Account to the Sign in with Apple-Account (as described here and here).
But for doing that I would need the error FIRAuthErrorUserInfoUpdatedCredentialKey that allows to retrieve the old user eventually.
In my case, I get ERROR_EMAIL_ALREADY_IN_USE which does not lead to any old user to be linked.
What do I have to do ?
Here is my code:
let credential = OAuthProvider.credential(withProviderID: "apple.com", idToken: idTokenString, rawNonce: nonce)
Auth.auth().signIn(with: credential) { (authResult, error) in
if (error != nil) {
print(error?.localizedDescription as Any)
return
}
print("signed in with Apple...")
do {
// if user did log in with Email/Password previously
if let email = try THKeychain.getEmail(),
let password = try THKeychain.getPassword() {
let credential = EmailAuthProvider.credential(withEmail: email, password: password)
if let user = authResult?.user {
// here I am trying to link the existing Firebase-Email/Password account to the just signed-in with Apple account
user.link(with: credential) { (result, linkError) in
print(linkError) // this is where I get FIRAuthErrorUserInfoNameKey=ERROR_EMAIL_ALREADY_IN_USE
// unfortunately, the two accounts are not linked as expected due to this error !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
// What is missing ??????????????????
loginStatus = true
}
}
} else {
loginStatus = true
}
} catch {
print(error.localizedDescription)
}
}
On the Firebase-documentation it sais:
Sign in with Apple will not allow you to reuse an auth credential to link to an existing account. If you want to link a Sign in with Apple credential to another account, you must first attempt to link the accounts using the old Sign in with Apple credential and then examine the error returned to find a new credential. The new credential will be located in the error's userInfo dictionary and can be accessed via the FIRAuthErrorUserInfoUpdatedCredentialKey key.
What does the part "...If you want to link a Sign in with Apple credential to another account, you must first attempt to link the accounts using the old Sign in with Apple credential..." exactly mean ? WHAT IS THE old Sign in with Apple credential ????????
And how would I do that ?
In fact, at the linking-call, I actually expected some sort of linkError.userInfo with an updated user to sign in with. But the linkError in my example only gives me the ERROR_EMAIL_ALREADY_IN_USE error without further userInfo.
As Peter Friese mentions in his Blog, I should somehow be able to retrieve a AuthErrorUserInfoUpdatedCredentialKey from the error.userInfo. But in my case, the linkError does not have any kind of such information - unfortunately!
Here is an excerpt of Peter's example: (again not applicable in my case for some unknown reason?????)
currentUser.link(with: credential) { (result, error) in // (1)
if let error = error, (error as NSError).code == AuthErrorCode.credentialAlreadyInUse.rawValue { // (2)
print("The user you're signing in with has already been linked, signing in to the new user and migrating the anonymous users [\(currentUser.uid)] tasks.")
if let updatedCredential = (error as NSError).userInfo[AuthErrorUserInfoUpdatedCredentialKey] as? OAuthCredential {
print("Signing in using the updated credentials")
Auth.auth().signIn(with: updatedCredential) { (result, error) in
if let user = result?.user {
// TODO: handle data migration
self.doSignIn(appleIDCredential: appleIDCredential, user: user) // (3)
}
}
}
}
}

Answer 1

Reversing the order of linking made me advance a tiny bit.
If I press the Sign in with Apple button, my code now logs in with Firebase-Email/Password first (i.e. the necessary credentials are taken from the Keychain). And on a second step, links with the Apple-credentials. And by doing so, the linking finally gives me the desired AuthErrorUserInfoUpdatedCredentialKey in the link-callback.
There I retrieve the updatedCredential to log in with Apple.
See code below.
HOWEVER, I STILL DON'T KNOW WHY AFTER LOGIN THIS WAY, MY DATA IS STILL MISSING ???????
HOW DOES THIS DATA-MIGRATION STEP WORK ???
Shouldn't the user.link(with: appleCredentials) { ... } do the job ?
What do I need to do in order to get the very same Firebase-Data, no matter the login method ???
let appleCredentials = OAuthProvider.credential(withProviderID: "apple.com", idToken: idTokenString, rawNonce: nonce)
do {
// if user did log in with Email/Password anytime before
if let email = try THKeychain.getEmail(),
let password = try THKeychain.getPassword() {
let firebaseEmailCredentials = EmailAuthProvider.credential(withEmail: email, password: password)
Auth.auth().signIn(with: firebaseEmailCredentials) { (authResult, error) in
if let user = authResult?.user {
user.link(with: appleCredentials) { (result, linkError) in
if let linkError = linkError, (linkError as NSError).code == AuthErrorCode.credentialAlreadyInUse.rawValue {
print("The user you're signing in with has been linked.")
print("Signing in to Apple and migrating the email/pw-firebase-users [\(user.uid)]` data.")
if let updatedCredential = (linkError as NSError).userInfo[AuthErrorUserInfoUpdatedCredentialKey] as? OAuthCredential {
print("Signing in using the updated credentials")
Auth.auth().signIn(with: updatedCredential) { (result, error) in
if let _ = result?.user {
print("signed in with Apple...")
// TODO: handle data migration
print("Data-migration takes place now...")
loginStatus = true
}
}
}
}
else if let error = error {
print("Error trying to link user: \(error.localizedDescription)")
}
else {
if let _ = result?.user {
loginStatus = true
}
}
}
}
}
} else {
// case where user never logged in with firebase-Email/Password before
Auth.auth().signIn(with: appleCredentials) { (result, error) in
if let _ = result?.user {
print("signed in with Apple...")
loginStatus = true
}
}
}
} catch {
print(error.localizedDescription)
}