You can let your users authenticate with Firebase using their Facebook accounts by integrating Facebook Login or Facebook Limited Login into your app.
Before you begin
Use Swift Package Manager to install and manage Firebase dependencies.
- In Xcode, with your app project open, navigate to File > Add Packages.
- When prompted, add the Firebase Apple platforms SDK repository:
- Choose the Firebase Authentication library.
- When finished, Xcode will automatically begin resolving and downloading your dependencies in the background.
https://github.com/firebase/firebase-ios-sdk
Next, perform some configuration steps:
- On the Facebook for Developers site, get the App ID and an App Secret for your app.
- Enable Facebook Login:
- In the Firebase console, open the Auth section.
- On the Sign in method tab, enable the Facebook sign-in method and specify the App ID and App Secret you got from Facebook.
- Then, make sure your OAuth redirect URI (e.g.
my-app-12345.firebaseapp.com/__/auth/handler) is listed as one of your OAuth redirect URIs in your Facebook app's settings page on the Facebook for Developers site in the Product Settings > Facebook Login config.
Implement Facebook Login
To use "classic" Facebook Login, complete the following steps. Alternatively, you can use Facebook Limited Login, as shown in the next section.
- Integrate Facebook Login into your app by following the
developer's documentation. When you initialize the
FBSDKLoginButtonobject, set a delegate to receive login and logout events. For example:In your delegate, implementSwift
let loginButton = FBSDKLoginButton() loginButton.delegate = self
Objective-C
FBSDKLoginButton *loginButton = [[FBSDKLoginButton alloc] init]; loginButton.delegate = self;
didCompleteWithResult:error:.Swift
func loginButton(_ loginButton: FBSDKLoginButton!, didCompleteWith result: FBSDKLoginManagerLoginResult!, error: Error!) { if let error = error { print(error.localizedDescription) return } // ... }Objective-C
- (void)loginButton:(FBSDKLoginButton *)loginButton didCompleteWithResult:(FBSDKLoginManagerLoginResult *)result error:(NSError *)error { if (error == nil) { // ... } else { NSLog(error.localizedDescription); } } - Import the
FirebaseCoremodule in yourUIApplicationDelegate, as well as any other Firebase modules your app delegate uses. For example, to use Cloud Firestore and Authentication:Swift
import FirebaseCore import FirebaseFirestore import FirebaseAuth // ...Objective-C
@import FirebaseCore; @import FirebaseFirestore; @import FirebaseAuth; // ... - Configure a
FirebaseAppshared instance, typically in yourApp's initializer or app delegate'sapplication(_:didFinishLaunchingWithOptions:)method:Swift
// Use Firebase library to configure APIs FirebaseApp.configure()
Objective-C
// Use Firebase library to configure APIs [FIRApp configure];
- After a user successfully signs in, in your implementation of
didCompleteWithResult:error:, get an access token for the signed-in user and exchange it for a Firebase credential:Swift
let credential = FacebookAuthProvider .credential(withAccessToken: AccessToken.current!.tokenString)
Objective-C
FIRAuthCredential *credential = [FIRFacebookAuthProvider credentialWithAccessToken:[FBSDKAccessToken currentAccessToken].tokenString];
Implement Facebook Limited Login
To use Facebook Limited Login instead of "classic" Facebook Login, complete the following steps.
- Integrate Facebook Limited Login into your app by following the developer's documentation.
- For every sign-in request, generate a unique random string—a "nonce"—which
you will use to make sure the ID token you get was granted specifically in
response to your app's authentication request. This step is important to
prevent replay attacks.
You can generate a cryptographically secure nonce with
SecRandomCopyBytes(_:_:_), as in the following example:You will send the SHA-256 hash of the nonce with your sign-in request, which Facebook will pass unchanged in the response. Firebase validates the response by hashing the original nonce and comparing it to the value passed by Facebook.Swift
// Adapted from https://auth0.com/docs/api-auth/tutorials/nonce#generate-a-cryptographically-random-nonce private func randomNonceString(length: Int = 32) -> String { precondition(length > 0) let charset: [Character] = Array("0123456789ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz-._") var result = "" var remainingLength = length while remainingLength > 0 { let randoms: [UInt8] = (0 ..< 16).map { _ in var random: UInt8 = 0 let errorCode = SecRandomCopyBytes(kSecRandomDefault, 1, &random) if errorCode != errSecSuccess { fatalError( "Unable to generate nonce. SecRandomCopyBytes failed with OSStatus \(errorCode)" ) } return random } randoms.forEach { random in if remainingLength == 0 { return } if random < charset.count { result.append(charset[Int(random)]) remainingLength -= 1 } } } return result }Objective-C
// Adapted from https://auth0.com/docs/api-auth/tutorials/nonce#generate-a-cryptographically-random-nonce - (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 copy]; }Swift
@available(iOS 13, *) private func sha256(_ input: String) -> String { let inputData = Data(input.utf8) let hashedData = SHA256.hash(data: inputData) let hashString = hashedData.compactMap { String(format: "%02x", $0) }.joined() return hashString }Objective-C
- (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; } - When you set up the
FBSDKLoginButton, set a delegate to receive login and logout events, set the tracking mode toFBSDKLoginTrackingLimited, and attach a nonce. For example:In your delegate, implementSwift
func setupLoginButton() { let nonce = randomNonceString() currentNonce = nonce loginButton.delegate = self loginButton.loginTracking = .limited loginButton.nonce = sha256(nonce) }Objective-C
- (void)setupLoginButton { NSString *nonce = [self randomNonce:32]; self.currentNonce = nonce; self.loginButton.delegate = self; self.loginButton.loginTracking = FBSDKLoginTrackingLimited self.loginButton.nonce = [self stringBySha256HashingString:nonce]; }didCompleteWithResult:error:.Swift
func loginButton(_ loginButton: FBSDKLoginButton!, didCompleteWith result: FBSDKLoginManagerLoginResult!, error: Error!) { if let error = error { print(error.localizedDescription) return } // ... }Objective-C
- (void)loginButton:(FBSDKLoginButton *)loginButton didCompleteWithResult:(FBSDKLoginManagerLoginResult *)result error:(NSError *)error { if (error == nil) { // ... } else { NSLog(error.localizedDescription); } } - Import the
FirebaseCoremodule in yourUIApplicationDelegate, as well as any other Firebase modules your app delegate uses. For example, to use Cloud Firestore and Authentication:Swift
import FirebaseCore import FirebaseFirestore import FirebaseAuth // ...Objective-C
@import FirebaseCore; @import FirebaseFirestore; @import FirebaseAuth; // ... - Configure a
FirebaseAppshared instance, typically in yourApp's initializer or app delegate'sapplication(_:didFinishLaunchingWithOptions:)method:Swift
// Use Firebase library to configure APIs FirebaseApp.configure()
Objective-C
// Use Firebase library to configure APIs [FIRApp configure];
- After a user successfully signs in, in your implementation of
didCompleteWithResult:error:, use the ID token from Facebook's response with the unhashed nonce to get a Firebase credential:Swift
// Initialize a Firebase credential. let idTokenString = AuthenticationToken.current?.tokenString let nonce = currentNonce let credential = OAuthProvider.credential(withProviderID: "facebook.com", idToken: idTokenString!, rawNonce: nonce)Objective-C
// Initialize a Firebase credential. NSString *idTokenString = FBSDKAuthenticationToken.currentAuthenticationToken.tokenString; NSString *rawNonce = self.currentNonce; FIROAuthCredential *credential = [FIROAuthProvider credentialWithProviderID:@"facebook.com" IDToken:idTokenString rawNonce:rawNonce];
Authenticate with Firebase
Finally, authenticate with Firebase using the Firebase credential:
Swift
Auth.auth().signIn(with: credential) { authResult, error in
if let error = error {
let authError = error as NSError
if isMFAEnabled, authError.code == AuthErrorCode.secondFactorRequired.rawValue {
// The user is a multi-factor user. Second factor challenge is required.
let resolver = authError
.userInfo[AuthErrorUserInfoMultiFactorResolverKey] as! MultiFactorResolver
var displayNameString = ""
for tmpFactorInfo in resolver.hints {
displayNameString += tmpFactorInfo.displayName ?? ""
displayNameString += " "
}
self.showTextInputPrompt(
withMessage: "Select factor to sign in\n\(displayNameString)",
completionBlock: { userPressedOK, displayName in
var selectedHint: PhoneMultiFactorInfo?
for tmpFactorInfo in resolver.hints {
if displayName == tmpFactorInfo.displayName {
selectedHint = tmpFactorInfo as? PhoneMultiFactorInfo
}
}
PhoneAuthProvider.provider()
.verifyPhoneNumber(with: selectedHint!, uiDelegate: nil,
multiFactorSession: resolver
.session) { verificationID, error in
if error != nil {
print(
"Multi factor start sign in failed. Error: \(error.debugDescription)"
)
} else {
self.showTextInputPrompt(
withMessage: "Verification code for \(selectedHint?.displayName ?? "")",
completionBlock: { userPressedOK, verificationCode in
let credential: PhoneAuthCredential? = PhoneAuthProvider.provider()
.credential(withVerificationID: verificationID!,
verificationCode: verificationCode!)
let assertion: MultiFactorAssertion? = PhoneMultiFactorGenerator
.assertion(with: credential!)
resolver.resolveSignIn(with: assertion!) { authResult, error in
if error != nil {
print(
"Multi factor finanlize sign in failed. Error: \(error.debugDescription)"
)
} else {
self.navigationController?.popViewController(animated: true)
}
}
}
)
}
}
}
)
} else {
self.showMessagePrompt(error.localizedDescription)
return
}
// ...
return
}
// User is signed in
// ...
}
Objective-C
[[FIRAuth auth] signInWithCredential:credential
completion:^(FIRAuthDataResult * _Nullable authResult,
NSError * _Nullable error) {
if (isMFAEnabled && error && error.code == FIRAuthErrorCodeSecondFactorRequired) {
FIRMultiFactorResolver *resolver = error.userInfo[FIRAuthErrorUserInfoMultiFactorResolverKey];
NSMutableString *displayNameString = [NSMutableString string];
for (FIRMultiFactorInfo *tmpFactorInfo in resolver.hints) {
[displayNameString appendString:tmpFactorInfo.displayName];
[displayNameString appendString:@" "];
}
[self showTextInputPromptWithMessage:[NSString stringWithFormat:@"Select factor to sign in\n%@", displayNameString]
completionBlock:^(BOOL userPressedOK, NSString *_Nullable displayName) {
FIRPhoneMultiFactorInfo* selectedHint;
for (FIRMultiFactorInfo *tmpFactorInfo in resolver.hints) {
if ([displayName isEqualToString:tmpFactorInfo.displayName]) {
selectedHint = (FIRPhoneMultiFactorInfo *)tmpFactorInfo;
}
}
[FIRPhoneAuthProvider.provider
verifyPhoneNumberWithMultiFactorInfo:selectedHint
UIDelegate:nil
multiFactorSession:resolver.session
completion:^(NSString * _Nullable verificationID, NSError * _Nullable error) {
if (error) {
[self showMessagePrompt:error.localizedDescription];
} else {
[self showTextInputPromptWithMessage:[NSString stringWithFormat:@"Verification code for %@", selectedHint.displayName]
completionBlock:^(BOOL userPressedOK, NSString *_Nullable verificationCode) {
FIRPhoneAuthCredential *credential =
[[FIRPhoneAuthProvider provider] credentialWithVerificationID:verificationID
verificationCode:verificationCode];
FIRMultiFactorAssertion *assertion = [FIRPhoneMultiFactorGenerator assertionWithCredential:credential];
[resolver resolveSignInWithAssertion:assertion completion:^(FIRAuthDataResult * _Nullable authResult, NSError * _Nullable error) {
if (error) {
[self showMessagePrompt:error.localizedDescription];
} else {
NSLog(@"Multi factor finanlize sign in succeeded.");
}
}];
}];
}
}];
}];
}
else if (error) {
// ...
return;
}
// User successfully signed in. Get user data from the FIRUser object
if (authResult == nil) { return; }
FIRUser *user = authResult.user;
// ...
}];
Next steps
After a user signs in for the first time, a new user account is created and linked to the credentials—that is, the user name and password, phone number, or auth provider information—the user signed in with. This new account is stored as part of your Firebase project, and can be used to identify a user across every app in your project, regardless of how the user signs in.
-
In your apps, you can get the user's basic profile information from the
FIRUserobject. See Manage Users. In your Firebase Realtime Database and Cloud Storage Security Rules, you can get the signed-in user's unique user ID from the
authvariable, and use it to control what data a user can access.
You can allow users to sign in to your app using multiple authentication providers by linking auth provider credentials to an existing user account.
To sign out a user, call
signOut:.
Swift
let firebaseAuth = Auth.auth()
do {
try firebaseAuth.signOut()
} catch let signOutError as NSError {
print("Error signing out: %@", signOutError)
}
Objective-C
NSError *signOutError;
BOOL status = [[FIRAuth auth] signOut:&signOutError];
if (!status) {
NSLog(@"Error signing out: %@", signOutError);
return;
}
You may also want to add error handling code for the full range of authentication errors. See Handle Errors.