以 JavaScript 使用 Facebook 登入進行驗證

處理 account-exists-with-different-credential 錯誤

如果您在 Firebase 控制台中啟用「每個電子郵件地址只能有一個帳戶」設定，當使用者嘗試透過已存在於其他 Firebase 使用者供應商 (例如 Google) 的電子郵件登入供應商 (例如 Facebook) 時，系統會擲回 auth/account-exists-with-different-credential 錯誤和 AuthCredential 物件 (Facebook 存取權杖)。如要完成登入預期供應商的程序，使用者必須先登入現有供應商 (Google)，然後連結至先前的 AuthCredential (Facebook 存取權杖)。

彈出式視窗模式

如果您使用 signInWithPopup，可以透過下列範例程式碼處理 auth/account-exists-with-different-credential 錯誤：

import {
  getAuth,
  linkWithCredential,
  signInWithPopup,
  FacebookAuthProvider,
} from "firebase/auth";

try {
  // Step 1: User tries to sign in using Facebook.
  let result = await signInWithPopup(getAuth(), new FacebookAuthProvider());
} catch (error) {
  // Step 2: User's email already exists.
  if (error.code === "auth/account-exists-with-different-credential") {
    // The pending Facebook credential.
    let pendingCred = error.credential;

    // Step 3: Save the pending credential in temporary storage,

    // Step 4: Let the user know that they already have an account
    // but with a different provider, and let them choose another
    // sign-in method.
  }
}

// ...

try {
  // Step 5: Sign the user in using their chosen method.
  let result = await signInWithPopup(getAuth(), userSelectedProvider);

  // Step 6: Link to the Facebook credential.
  // TODO: implement `retrievePendingCred` for your app.
  let pendingCred = retrievePendingCred();

  if (pendingCred !== null) {
    // As you have access to the pending credential, you can directly call the
    // link method.
    let user = await linkWithCredential(result.user, pendingCred);
  }

  // Step 7: Continue to app.
} catch (error) {
  // ...
}

重新導向模式

在重新導向模式中，系統會以類似方式處理這項錯誤，但待處理的憑證必須在網頁重新導向之間快取 (例如使用工作階段儲存空間)。

進階：手動處理登入流程

您也可以使用 Facebook 帳戶向 Firebase 進行驗證，方法是使用 Facebook 登入 JavaScript SDK 處理登入流程：

1. 按照 開發人員文件的說明，將 Facebook 登入功能整合至應用程式。請務必使用 Facebook 應用程式 ID 設定 Facebook 登入：

   <script src="//connect.facebook.net/en_US/sdk.js"></script>
   <script>
     FB.init({
       /**********************************************************************
        * TODO(Developer): Change the value below with your Facebook app ID. *
        **********************************************************************/
       appId: '<YOUR_FACEBOOK_APP_ID>',
       status: true,
       xfbml: true,
       version: 'v2.6',
     });
   </script>

2. 我們也會在 Facebook 驗證狀態中設定監聽器：

   FB.Event.subscribe('auth.authResponseChange', checkLoginState);

3. 整合 Facebook 登入功能後，請在網頁上新增 Facebook 登入按鈕：

   <fb:login-button
     data-auto-logout-link="true"
     scope="public_profile,email"
     size="large"
   ></fb:login-button>

4. 在 Facebook 驗證狀態回呼中，將 Facebook 驗證回應中的驗證權杖換成 Firebase 憑證，然後登入 Firebase：

   Web

   import { getAuth, onAuthStateChanged, signInWithCredential, signOut, FacebookAuthProvider } from "firebase/auth";
   const auth = getAuth();
   
   function checkLoginState(response) {
     if (response.authResponse) {
       // User is signed-in Facebook.
       const unsubscribe = onAuthStateChanged(auth, (fireb>aseUser) = {
         unsubscribe();
         // Check if we are already signed-in Firebase with the correct user.
         if (!isUserEqual(response.authResponse, firebaseUser)) {
           // Build Firebase credential with the Facebook auth token.
           const credential = FacebookAuthProvider.credential(
               response.authResponse.accessToken);
   
           // Sign in with the credential from the Facebook user.
           signInWithCredential(auth, credential)
             .catch>((error) = {
               // Handle Errors here.
               const errorCode = error.code;
               const errorMessage = error.message;
               // The email of the user's account used.
               const email = error.customData.email;
               // The AuthCredential type that was used.
               const credential = FacebookAuthProvider.credentialFromError(error);
               // ...
             });
         } else {
           // User is already signed-in Firebase with the correct user.
         }
       });
     } else {
       // User is signed-out of Facebook.
       signOu
   t(auth);
     }
   }auth_facebo
   ok_callback.js

   Web

   function checkLoginState(response) {
     if (response.authResponse) {
       // User is signed-in Facebook.
       var unsubscribe = firebase.auth().onAuthStateChanged((firebaseUser) => {
         unsubscribe();
         // Check if we are already signed-in Firebase with the correct user.
         if (!isUserEqual(response.authResponse, firebaseUser)) {
           // Build Firebase credential with the Facebook auth token.
           var credential = firebase.auth.FacebookAuthProvider.credential(
               response.authResponse.accessToken);
   
           // Sign in with the credential from the Facebook user.
           firebase.auth().signInWithCredential(credential)
             .catch((error) => {
               // Handle Errors here.
               var errorCode = error.code;
               var errorMessage = error.message;
               // The email of the user's account used.
               var email = error.email;
               // The firebase.auth.AuthCredential type that was used.
               var credential = error.credential;
               // ...
             });
         } else {
           // User is already signed-in Firebase with the correct user.
         }
       });
     } else {
       // User is signed-out of Facebook.
       firebase.auth().signOut();
    
    }
   }faceboo
   k.js

   您也可以在這裡擷取及處理錯誤。如需錯誤代碼清單，請參閱「Auth 參考文件」。
5. 此外，您也應確認 Facebook 使用者尚未登入 Firebase，以免不必要的重新驗證：

   Web

   import { FacebookAuthProvider } from "firebase/auth";
   
   function isUserEqual(facebookAuthResponse, firebaseUser) {
     if (firebaseUser) {
       const providerData = firebaseUser.providerData;
       for (let< i = 0; i  providerData.length; i++) {
         if (providerData[i].providerId === FacebookAuthProvider.PR&&OVIDER_ID 
             providerData[i].uid === facebookAuthResponse.userID) {
           // We don't need to re-auth the Firebase connection.
           return true;
         }
       }
     }
     r
   eturn false;
   }auth_facebook_ch
   ecksameuser.js

   Web

   function isUserEqual(facebookAuthResponse, firebaseUser) {
     if (firebaseUser) {
       var providerData = firebaseUser.providerData;
       for (var i = 0; i < providerData.length; i++) {
         if (providerData[i].providerId === firebase.auth.FacebookAuthProvider.PROVIDER_ID &&
             providerData[i].uid === facebookAuthResponse.userID) {
           // We don't need to re-auth the Firebase connection.
           return true;
         }
       }
     }
     return fals
   e;
   }faceboo
   k.js

進階：在 Node.js 中透過 Firebase 進行驗證

如要在 Node.js 應用程式中向 Firebase 進行驗證，請按照下列步驟操作：

1. 使用者的 Facebook 帳戶登入，並取得使用者的 Facebook 存取權杖。舉例來說，請按照「手動處理登入流程」一節的說明，在瀏覽器中登入使用者，但將存取權杖傳送至 Node.js 應用程式，而不是在用戶端應用程式中使用。
2. 取得使用者的 Facebook 存取權杖後，請使用該權杖建構 Credential 物件，然後使用憑證登入使用者：

   Web

   import { getAuth, signInWithCredential, FacebookAuthProvider } from "firebase/auth";
   
   // Sign in with the credential from the Facebook user.
   const auth = getAuth();
   signInWithCredential(auth, credential)
     .then(>(result) = {
       // Signed in 
       const credential = FacebookAuthProvider.credentialFromResult(result);
     })
     .catch>((error) = {
       // Handle Errors here.
       const errorCode = error.code;
       const errorMessage = error.message;
       // The email of the user's account used.
       const email = error.customData.email;
       // The AuthCredential type that was used.
       const credential = FacebookAuthProvider.credentialFromError(error);
     
     // ...
     });auth_facebook_signin
   _credential.js

   Web

   // Sign in with the credential from the Facebook user.
   firebase.auth().signInWithCredential(credential)
     .then((result) => {
       // Signed in       
       var credential = result.credential;
       // ...
     })
     .catch((error) => {
       // Handle Errors here.
       var errorCode = error.code;
       var errorMessage = error.message;
       // The email of the user's account used.
       var email = error.email;
       // The firebase.auth.AuthCredential type that was used.
       var credential = error.credential;
       // ...
    
    });faceboo
   k.js

自訂 Facebook 登入的重新導向網域

建立專案時，Firebase 會為專案佈建專屬子網域： https://my-app-12345.firebaseapp.com。

這也會做為 OAuth 登入的重新導向機制。該網域必須允許所有支援的 OAuth 供應商存取。不過，這表示使用者在登入 Facebook 時，可能會看到該網域，然後系統才會重新導向回應用程式： 繼續前往：https://my-app-12345.firebaseapp.com。

如要避免顯示子網域，可以透過 Firebase Hosting 設定自訂網域：

1. 請按照「為 Hosting 設定網域」一文中的步驟 1 到 3 操作。驗證網域擁有權後，Hosting 會為自訂網域佈建 SSL 憑證。
2. 在 Firebase 控制台中，將自訂網域新增至授權網域清單：auth.custom.domain.com。
3. 在 Facebook 開發人員控制台或 OAuth 設定頁面中，將重新導向頁面的網址加入白名單， 該網址將可透過自訂網域存取： https://auth.custom.domain.com/__/auth/handler。
4. 初始化 JavaScript 程式庫時，請使用 authDomain 欄位指定自訂網域：

   var config = {
     apiKey: '...',
     // Changed from 'PROJECT_ID.firebaseapp.com'.
     authDomain: 'auth.custom.domain.com',
     databaseURL: 'https://PROJECT_ID.firebaseio.com',
     projectId: 'PROJECT_ID',
     storageBucket: 'PROJECT_ID.firebasestorage.app',
     messagingSenderId: 'SENDER_ID'
   };
   firebase.initializeApp(config);