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在 iOS 上让用户通过 Facebook 登录

您可以将 Facebook 登录服务或 Facebook 受限登录服务集成到您的应用中，让您的用户能够使用自己的 Facebook 账号进行 Identity Platform 身份验证。本页面介绍如何使用 Identity Platform 将“使用 Facebook 账号登录”添加到 iOS 应用。

准备工作

将 Firebase 添加到您的 iOS 项目。
在您的 Podfile 中添加以下 Pod：
```
pod 'FirebaseAuth'
```
前往 Google Cloud 控制台中的身份提供商页面。

转到“身份提供商”页面
点击添加提供商。
从列表中选择 Facebook。
输入您的 Facebook 应用 ID 和应用密钥。如果您还没有 ID 和密钥，则可以从 Facebook for Developers 页面获取一个。
将配置 Facebook 下列出的 URI 配置为您的 Facebook 应用的有效 OAuth 重定向 URI。如果您在 Identity Platform 中配置了自定义网域，请更新 Facebook 应用配置中的重定向 URI，以使用自定义网域（而非默认网域）。例如，将 https://myproject.firebaseapp.com/__/auth/handler 更改为 https://auth.myownpersonaldomain.com/__/auth/handler。
点击已获授权的网域下的添加网域，以注册您应用的网域。出于开发目的，localhost 默认处于启用状态。
在配置您的应用下，点击设置详情。将代码段复制到应用的代码中，以初始化 Identity Platform Client SDK。
点击保存。

实现 Facebook 登录

要使用“传统版”Facebook 登录，请完成以下步骤。或者，您也可以使用 Facebook 受限登录，如下一部分所示。

按开发者文档中的说明操作，将 Facebook 登录集成到您的应用中。当初始化 FBSDKLoginButton 对象时，设置一个委托 (delegate) 来接收登录和退出账号事件。例如：

Swift

let loginButton = FBSDKLoginButton()
loginButton.delegate = self

Objective-C

FBSDKLoginButton *loginButton = [[FBSDKLoginButton alloc] init];
loginButton.delegate = self;

在您的委托中，实现 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);
  }
}

在 UIApplicationDelegate 中导入 Firebase 模块：

Swift

import FirebaseCore
import FirebaseAuth

Objective-C

@import FirebaseCore;
@import FirebaseAuth;

配置一个 FirebaseApp 共享实例（通常在应用的 application:didFinishLaunchingWithOptions: 方法中配置）：
Swift
```
// Use Firebase library to configure APIs
FirebaseApp.configure()
```
Objective-C
```
// Use Firebase library to configure APIs
[FIRApp configure];
```

用户成功登录后，在 didCompleteWithResult:error: 的实现代码中为登录的用户获取一个访问令牌，然后用该访问令牌换取 Identity Platform 凭据：

Swift

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

Objective-C

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

实现 Facebook 受限登录

要使用 Facebook 受限登录（而非“传统版”Facebook 登录），请完成以下步骤。

按开发者文档中的说明操作，将 Facebook 受限登录集成到您的应用中。

为每个登录请求生成唯一的随机字符串（“随机数”），用来确保您获取的 ID 令牌专门用于响应您的应用的身份验证请求。此步骤对于防止重放攻击至关重要。您可以在 iOS 上使用 SecRandomCopyBytes(_:_:_) 生成加密的安全随机数，如以下示例所示：

Swift

private func randomNonceString(length: Int = 32) -> String {
  precondition(length > 0)
  var randomBytes = [UInt8](repeating: 0, count: length)
  let errorCode = SecRandomCopyBytes(kSecRandomDefault, randomBytes.count, &randomBytes)
  if errorCode != errSecSuccess {
    fatalError(
      "Unable to generate nonce. SecRandomCopyBytes failed with OSStatus \(errorCode)"
    )
  }

  let charset: [Character] =
    Array("0123456789ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz-._")

  let nonce = randomBytes.map { byte in
    // Pick a random character from the set, wrapping around if needed.
    charset[Int(byte) % charset.count]
  }

  return String(nonce)
}

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];
}

您将通过登录请求发送随机数的 SHA-256 哈希，Facebook 将在响应中原封不动地传递该值。Identity Platform 通过对原始随机数进行哈希处理并将其与 Facebook 传递的值进行比较来验证响应。

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;
}

设置 FBSDKLoginButton 时，设置一个委托来接收登录和退出登录事件，将跟踪模式设置为 FBSDKLoginTrackingLimited，并附加一个随机数。例如：

Swift

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];
}

在您的委托中，实现 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);
  }
}

在 UIApplicationDelegate 中导入 Firebase 模块：
Swift
```
import Firebase
```
Objective-C
```
@import Firebase;
```
配置一个 FirebaseApp 共享实例（通常在应用的 application:didFinishLaunchingWithOptions: 方法中配置）：
Swift
```
// Use Firebase library to configure APIs
FirebaseApp.configure()
```
Objective-C
```
// Use Firebase library to configure APIs
[FIRApp configure];
```

用户成功登录后，在 didCompleteWithResult:error: 实现中，使用 Facebook 响应中的 ID 令牌和未经哈希处理的随机数来获取 Identity Platform 凭据：

Swift

// Initialize an Identity Platform credential.
let idTokenString = AuthenticationToken.current?.tokenString
let nonce = currentNonce
let credential = OAuthProvider.credential(withProviderID: "facebook.com",
                                          IDToken: idTokenString,
                                          rawNonce: nonce)

Objective-C

// Initialize an Identity Platform credential.
NSString *idTokenString = FBSDKAuthenticationToken.currentAuthenticationToken.tokenString;
NSString *rawNonce = self.currentNonce;
FIROAuthCredential *credential = [FIROAuthProvider credentialWithProviderID:@"facebook.com"
                                                                    IDToken:idTokenString
                                                                   rawNonce:rawNonce];

使用 Identity Platform 进行身份验证

最后，使用 Identity Platform 凭据向 Identity Platform 进行身份验证：

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;
  // ...
}];

后续步骤

详细了解 Identity Platform 用户。
让用户通过其他身份提供商登录。