Why is apple sign-in with FirebaseUI not working?

House I have used the Apple Signin in an app but it is in Objective-c. The flow is very simple to test even in Objective-C if you are not used.

In the view with the login I added this sentence for delegate.

@import Firebase;
@import GoogleSignIn;

@interface loginViewController () <GIDSignInDelegate, ASAuthorizationControllerDelegate>

Then after a button tap I execute the AppleSignIn ASAuthorizationControllerDelegate flow like this:

- (IBAction)startSignInWithAppleFlow:(id)sender
{
    if (@available(iOS 13.0, *)) {
        NSString *nonce = [self randomNonce:32];
        self.currentNonce = nonce;
        ASAuthorizationAppleIDProvider *appleIDProvider = [[ASAuthorizationAppleIDProvider alloc] init];
        ASAuthorizationAppleIDRequest *request = [appleIDProvider createRequest];
        request.requestedScopes = @[ASAuthorizationScopeFullName, ASAuthorizationScopeEmail];
        request.nonce = [self stringBySha256HashingString:nonce];

        ASAuthorizationController *authorizationController = [[ASAuthorizationController alloc] initWithAuthorizationRequests:@[request]];
        authorizationController.delegate = self;
        authorizationController.presentationContextProvider = self;
        [authorizationController performRequests];
    }
}

- (NSString *)stringBySha256HashingString:(NSString *)input
{
    const char *string = [input UTF8String];
    unsigned char result[CC_SHA256_DIGEST_LENGTH];
    CC_SHA256(string, (CC_LONG)strlen(string), result);

    NSMutableString *hashed = [NSMutableString stringWithCapacity:CC_SHA256_DIGEST_LENGTH * 2];
    for (NSInteger i = 0; i < CC_SHA256_DIGEST_LENGTH; i++) {
        [hashed appendFormat:@"%02x", result[i]];
    }
    return hashed;
}

- (NSString *)randomNonce:(NSInteger)length
{
    NSAssert(length > 0, @"Expected nonce to have positive length");
    NSString *characterSet = @"0123456789ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz-._";
    NSMutableString *result = [NSMutableString string];
    NSInteger remainingLength = length;

    while (remainingLength > 0) {
        NSMutableArray *randoms = [NSMutableArray arrayWithCapacity:16];
        for (NSInteger i = 0; i < 16; i++) {
            uint8_t random = 0;
            int errorCode = SecRandomCopyBytes(kSecRandomDefault, 1, &random);
            NSAssert(errorCode == errSecSuccess, @"Unable to generate nonce: OSStatus %i", errorCode);

            [randoms addObject:@(random)];
        }

        for (NSNumber *random in randoms) {
            if (remainingLength == 0) {
                break;
            }

            if (random.unsignedIntValue < characterSet.length) {
                unichar character = [characterSet characterAtIndex:random.unsignedIntValue];
                [result appendFormat:@"%C", character];
                remainingLength--;
            }
        }
    }
    
    return result;
}

- (void)authorizationController:(ASAuthorizationController *)controller didCompleteWithAuthorization:(ASAuthorization *)authorization API_AVAILABLE(ios(13.0))
{
    if ([authorization.credential isKindOfClass:[ASAuthorizationAppleIDCredential class]]) {
        ASAuthorizationAppleIDCredential *appleIDCredential = authorization.credential;
        NSString *rawNonce = self.currentNonce;
        NSAssert(rawNonce != nil, @"Invalid state: A login callback was received, but no login request was sent.");

        if (appleIDCredential.identityToken == nil) {
            NSLog(@"Unable to fetch identity token.");
            return;
        }

        NSString *idToken = [[NSString alloc] initWithData:appleIDCredential.identityToken encoding:NSUTF8StringEncoding];
        if (idToken == nil) {
            NSLog(@"Unable to serialize id token from data: %@", appleIDCredential.identityToken);
        }

        // Initialize a Firebase credential.
        FIROAuthCredential *credential = [FIROAuthProvider credentialWithProviderID:@"apple.com"
                                                                            IDToken:idToken
                                                                           rawNonce:rawNonce];

        // Sign in with Firebase.
        [[FIRAuth auth] signInWithCredential:credential completion:^(FIRAuthDataResult * _Nullable authResult, NSError * _Nullable error) {
            if (error != nil) {
                // Error. If error.code == FIRAuthErrorCodeMissingOrInvalidNonce,
                // make sure you're sending the SHA256-hashed nonce as a hex string
                // with your request to Apple.
                
                NSLog(@"%ld - %@ - %@", error.code, error.description, error.localizedDescription);
                
                return;
            }
            // Sign-in succeeded!
            // User successfully signed in. Get user data from the FIRUser object
            if (authResult == nil) { return; }
            FIRUser *user = authResult.user;
            // ...
            NSLog(@"%@", user);
            
            // ...
            [[NSNotificationCenter defaultCenter] postNotificationName:@"LOGIN_SUCCESSFUL" object:nil];
            [self dismissViewControllerAnimated:YES completion:nil];
        }];
    }
}

- (void)authorizationController:(ASAuthorizationController *)controller didCompleteWithError:(NSError *)error API_AVAILABLE(ios(13.0))
{
    NSLog(@"Sign in with Apple errored: %@", error);
}

I don't know if you have follow the notes in this link: Apple Sign In with FireBase But if you follow them it should work in physical device, in simulator is not trivial make it work.

you have to add apple sign-in entitlements in your app bundle identifier from the apple developer account and from the apple developer account you have to download a key and upload that key to firebase and then your apple sign-in will start work, it is very common to create a key found on first searches of google very easily

use this example i hope it will work for you

        let authUI = FUIAuth.defaultAuthUI()
        authUI?.shouldHideCancelButton = true
        authUI?.delegate = delegate
        authUI?.tosurl = Constants.Url.kFirebaseTermsOfService
        authUI?.privacyPolicyURL = Constants.Url.kFirebasePrivacyPolicy
        
        let emailAuth = FUIEmailAuth()
        let facebookAuth = FUIFacebookAuth(permissions: ["public_profile", "email"])
        let googleAuth = FUIGoogleAuth()
        
        var providers: [FUIAuthProvider] = [emailAuth, facebookAuth, googleAuth]
        if useAnonymous {
            let anonymousAuth = FUIAnonymousAuth()
            providers.append(anonymousAuth)
        }

        if #available(iOS 13.0, *) {
            let appleAuth = FUIOAuth.appleAuthProvider()
            providers.append(appleAuth)
        }

        authUI?.providers = providers