在 Apple 平台上将多个身份验证提供方与一个帐号相关联

您可以通过将多个身份验证提供方凭据关联至现有用户帐号，让用户可以使用多个身份验证提供方登录您的应用。无论用户使用哪个身份验证提供方登录，系统均可通过同一 Firebase 用户 ID 识别用户。例如，使用密码登录的用户可以关联 Google 帐号，以后便可使用这两种方法中的任意一种登录。或者，匿名用户可以关联 Facebook 帐号，以后就可以使用 Facebook 帐号登录并继续使用您的应用。

准备工作

为您的应用增加对两个或多个身份验证提供方（可能包括匿名身份验证）的支持。

将身份验证提供方凭据与用户帐号关联

如需将身份验证提供方凭据与现有用户帐号关联，请按以下步骤操作：

1. 使用任意身份验证提供方或方法让用户登录。
2. 按照新身份验证提供方的登录流程逐步进行，直到需要调用某一 FIRAuth.signInWith 方法时停止。例如：获取用户的 Google ID 令牌、Facebook 访问令牌或电子邮件地址和密码。

3. 为此新身份验证提供方获取 FIRAuthCredential：

   Google 登录

   Swift

   guard
     let authentication = user?.authentication,
     let idToken = authentication.idToken
   else {
     return
   }
   
   let credential = GoogleAuthProvider.credential(withIDToken: idToken,
                                                  accessToken: authentication.accessToken)
   

   Objective-C

   FIRAuthCredential *credential =
   [FIRGoogleAuthProvider credentialWithIDToken:result.user.idToken.tokenString
                                    accessToken:result.user.accessToken.tokenString];
   

   Facebook 登录

   Swift

   let credential = FacebookAuthProvider
     .credential(withAccessToken: AccessToken.current!.tokenString)
   

   Objective-C

   FIRAuthCredential *credential = [FIRFacebookAuthProvider
       credentialWithAccessToken:[FBSDKAccessToken currentAccessToken].tokenString];
   

   电子邮件地址/密码登录

   Swift

   let credential = EmailAuthProvider.credential(withEmail: email, password: password)
   

   Objective-C

   FIRAuthCredential *credential =
       [FIREmailAuthProvider credentialWithEmail:email
                                                password:password];
   

4. 将 FIRAuthCredential 对象传递给已登录用户的 linkWithCredential:completion: 方法：

   Swift

       user.link(with: credential) { authResult, error in
     // ...
   }
   }
   

   Objective-C

       [[FIRAuth auth].currentUser linkWithCredential:credential
       completion:^(FIRAuthDataResult *result, NSError *_Nullable error) {
     // ...
   }];
   

   如果凭据已与另一用户帐号关联，则 linkWithCredential:completion: 调用将会失败。在这种情况下，您必须根据需要为您的应用合并帐号和相关数据：

   Swift

   let prevUser = Auth.auth().currentUser
   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
       // ...
   }
               // Merge prevUser and currentUser accounts and data
               // ...
           }
   

   Objective-C

   FIRUser *prevUser = [FIRAuth auth].currentUser;
   [[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;
     // ...
   }];
                                       // Merge prevUser and currentUser accounts and data
                                       // ...
                                   }];
   

如果对 linkWithCredential:completion: 的调用成功，用户现在便可使用关联的任意身份验证提供方服务进行登录，并访问相同的 Firebase 数据。

取消身份验证提供方与用户帐号的关联

您可以取消身份验证提供方与帐号的关联，这样用户就无法再通过该提供方登录了。

如需取消身份验证提供方与用户帐号的关联，请将提供方 ID 传递给 unlink 方法。您可以从 providerData 属性中获取与用户相关联的身份验证提供方的 ID。

Swift

Auth.auth().currentUser?.unlink(fromProvider: providerID!) { user, error in
  // ...
}

Objective-C

[[FIRAuth auth].currentUser unlinkFromProvider:providerID
                                    completion:^(FIRUser *_Nullable user, NSError *_Nullable error) {
  // ...
}];