Facebook 身份验证“已存在具有相同电子邮件地址但登录凭据不同的帐户”

如何解决Facebook 身份验证“已存在具有相同电子邮件地址但登录凭据不同的帐户”

我有多个登录选项供用户选择：电子邮件、谷歌和 Facebook。如果 Firebase 已将电子邮件存储为用户（即用户之前使用 [e-mail] 注册），则会出现一个提醒，告知用户使用该电子邮件的帐户已存在。这非常适用于 Google 登录，如此 screenshot 所示。但是，当用户单击 Facebook 按钮（甚至不切换屏幕）时，视觉上没有任何反应，并且我在调试器中收到此错误：

Error Domain=FIRAuthErrorDomain Code=17012 "An account already exists with
the same email address but different sign-in credentials. Sign in using a
provider associated with this email address." UserInfo={FIRAuthErrorUserInfoNameKey=ERROR_ACCOUNT_EXISTS_WITH_DIFFERENT_CREDENTIAL,FIRAuthErrorUserInfoEmailKey=[e-mail],FIRAuthErrorUserInfoUpdatedCredentialKey=<FIROAuthCredential:
0x6000005f3200>,NSLocalizedDescription=An account already exists with the
same email address but different sign-in credentials. Sign in using a
provider associated with this email address.}

这是我的登录视图控制器代码：

    override func viewDidLoad() {
        super.viewDidLoad()
        
        setUpFBButton()
        setUpGoogleButton()
        setUpEmailButton()
            
        GIDSignIn.sharedInstance()?.presentingViewController = self
    }
    
    
    
// MARK: - SIGN UP WITH GOOGLE
    func sign(_ signIn: GIDSignIn!,didSignInFor user: GIDGoogleUser!,withError error: Error!) {
        
        if let err = error {
            print("Failed to log into Google: ",err)
            return
        }
        print("Successfully logged into Google")
        
        guard let authentication = user.authentication else { return }
        let credential = GoogleAuthProvider.credential(withIDToken: authentication.idToken,accessToken: authentication.accessToken)
        
        // sign user in with Firebase
        Auth.auth().signIn(with: credential,completion: { (user,error) in
            let firstName = user?.user.displayName
            let email = user?.user.email
            let lastName = ""
            let uid = user?.user.uid
            
            if let err = error {
                print("Failed to create a Firebase User with Google account: ",err)
                return
            } else {
                // Successfully logged in
                print("Successfully logged into Firebase with Google email: ",email ?? "","Now add user to Firestore if user is new.")
                
                // check if user already exists
                self.addUserToFirestore(firstName ?? "",lastName,uid ?? "","Google")
                    }
                })
            }
    
            
        fileprivate func setUpGoogleButton() {
            Utilities.styleLightFilledButton(signInGoogleButton)
            signInGoogleButton!.addTarget(self,action:
                                #selector(handleCustomGoogleSignIn),for: .touchUpInside)
            
            GIDSignIn.sharedInstance()?.delegate = self
            }
        
        @objc func handleCustomGoogleSignIn() {
            GIDSignIn.sharedInstance().signIn()
            }
    
    
    
    
// MARK: - SIGN UP WITH FACEBOOK
    
    // design the facebook button and assign #selector to facebook button actions
    fileprivate func setUpFBButton() {
        Utilities.styleHollowButton(signInFacebookButton)
        
        signInFacebookButton.addTarget(self,action: #selector(handleCustomFBButton),for: .touchUpInside)
    }
    
    // handle the facebook button actions
    @objc func handleCustomFBButton() {
        LoginManager().logIn(permissions: ["email","public_profile"],from: self) { (result,err) in
            if err != nil {
                print("Custom FB login failed:",err!)
                return
            }
            self.getUserInfo()
        }
    }
    
    // grab id,name,and email of user
    func getUserInfo() {
        print("Successfully logged in with facebook...")
        GraphRequest(graphPath: "/me",parameters: ["fields": "id,email"]).start {
            (connection,result,err) in
            guard let Info = result as? [String: Any] else { return }
                let name = Info["name"] as? String
                let email = Info["email"] as? String
                let uid = Info["id"] as? String
            
            if err != nil {
                print("Failed to start graph request:",err!)
                return
            }
            print(result!)
            self.signIntoFirebase(name ?? "",uid ?? "")
            
        }
    }
    
    // connect the user to firebase
    func signIntoFirebase(_ name:String,_ email:String,_ uid:String) {
           let credential = FacebookAuthProvider.credential(withAccessToken: AccessToken.current!.tokenString)
            Auth.auth().signIn(with: credential) { (user,error) in
                if let err = error {
                    print(err)
                    return
                } else {
            print("Facebook user successfully authenticated with Firebase. Now run through Firestore.")
            // check if user already exists. if user exists,go to chats screen. if it does not exist,create a new user and redirect to chat screen.
                    self.addUserToFirestore(name,"",email,uid,"Facebook")
                    
                }
            }
        }
    
    
    func loginButtonDidLogOut(_ loginButton: FBLoginButton) {
        print("Logged out of facebook")
    }
    
    
    
// MARK: - Other functions
    
    func addUserToFirestore(_ firstName:String,_ lastName:String,_ uid:String,_ signInMethod:String) {
        let db = Firestore.firestore()
        let docRef = db.collection("users").document(uid)
        // check if user exists in firestore
        docRef.getDocument { (document,error) in
            if let document = document {
               if document.exists {
                let message = "Good news! You already have a Coal account that uses " + email + ".\nPlease sign in to your existing account. Then you will be able to link your " + signInMethod + " profile from your Account Settings page."
                // user exists. send to chats screen.
                print("User already exists. Document data: \(String(describing: document.data()))")
                self.showError("You're already a member!",message)
              } else {
                // user does not exist. create a new user
                 print("Document does not exist. Create new user.")
                
                docRef.setData(["firstname":firstName,"lastname":lastName,"email":email]) { err in
                    if err != nil {
                        // Show error message
                        print("Error saving user data to Firestore")
                    } else {
                        print("New user created in Firestore")
                        self.transitionToConvo()
                    }
                }
              }
            }
        }
    }
    
    func showError(_ title:String,_ message:String) {
        
        let alert = UIAlertController(title: title,message: message,preferredStyle: UIAlertController.Style.alert)
        alert.addAction(UIAlertAction(title: "Ok",style: UIAlertAction.Style.default,handler: nil))
        self.present(alert,animated: true,completion: nil)
    }
    
    func transitionToConvo() {
        let tabBarC = self.storyboard?.instantiateViewController(withIdentifier: "mainTabBarController") as! TabBarController
        tabBarC.modalPresentationStyle = .fullScreen
        self.present(tabBarC,completion: nil)
        print("Switched to TabBarController")
    }
    
    func setUpEmailButton() {
        Utilities.styleDarkFilledButton(signInEmailButton)
    }
    
    
} // end

我认为没有收到警报的原因是 Facebook uid 与 Firestore 中保存的电子邮件 uid 不匹配（而 Google uid 匹配）。我让警报显示的方式是 uid 是否与 Firestore 中的匹配，因此，警报不会显示。有谁知道我如何获得警报以显示如何不收到此错误？

我知道我的代码有点乱，所以如果你需要进一步的解释，请告诉我。任何帮助表示赞赏！

解决方法

经过数小时试图找出我的问题后，我决定发布一个问题......但几乎立即找到了答案（我知道是对的：/）。

由于已在项目设置中启用每封电子邮件一个帐户，Auth.auth().signIn 会自动扫描是否存在用户。如果用户存在，它将在 if error != nil 后返回错误。因为它在调用我的 addUserToFirestore 函数之前返回了错误（检查用户是否存在，如果不存在，则将用户添加到 Firestore），因此从未显示警报。

既然我们知道 if error != nil 是什么意思，我们可以在那里插入警报：

Auth.auth().signIn(with: credential) { (user,error) in
                if error != nil {
                    let message = "Good news! You already have a Coal account that uses " + email + ".\nPlease sign in to your existing account. Then you will be able to link your Facebook profile from your Account Settings page."
                    // user exists. send to chats screen.
                    print("User already exists. Let user know.")
                    self.showError("You're already a member!",message)
                    return
                }

我不知道为什么它适用于 Google Auth，但最终这适用于 Facebook Auth。