使用自訂聲明和安全規則控制訪問

Firebase Admin SDK 支持在用戶帳戶上定義自定義屬性。這提供了在 Firebase 應用中實施各種訪問控制策略的能力，包括基於角色的訪問控制。這些自定義屬性可以為用戶提供不同級別的訪問權限（角色），這些權限在應用程序的安全規則中強制執行。

可以為以下常見情況定義用戶角色：

• 授予用戶訪問數據和資源的管理權限。
• 定義用戶所屬的不同組。
• 提供多級訪問：
  • 區分付費/未付費用戶。
  • 將版主與普通用戶區分開來。
  • 教師/學生申請等
• 為用戶添加附加標識符。例如，Firebase 用戶可以映射到另一個系統中的不同 UID。

讓我們考慮一個您想要限制對數據庫節點“adminContent”的訪問的情況。您可以通過在管理員用戶列表中查找數據庫來做到這一點。但是，您可以使用名為admin的自定義用戶聲明和以下實時數據庫規則更有效地實現相同的目標：

{
  "rules": {
    "adminContent": {
      ".read": "auth.token.admin === true",
      ".write": "auth.token.admin === true",
    }
  }
}

自定義用戶聲明可通過用戶的身份驗證令牌訪問。在上面的示例中，只有在其令牌聲明中將admin設置為 true 的用戶才具有對adminContent節點的讀/寫訪問權限。由於 ID 令牌已經包含這些斷言，因此不需要額外的處理或查找來檢查管理員權限。此外，ID 令牌是交付這些自定義聲明的可信機制。所有經過身份驗證的訪問都必須在處理相關請求之前驗證 ID 令牌。

本頁中描述的代碼示例和解決方案來自Admin SDK提供的客戶端 Firebase Auth API 和服務器端 Auth API。

通過 Admin SDK 設置和驗證自定義用戶聲明

自定義聲明可能包含敏感數據，因此它們只能由 Firebase Admin SDK 從特權服務器環境中設置。

// Set admin privilege on the user corresponding to uid.

getAuth()
  .setCustomUserClaims(uid, { admin: true })
  .then(() => {
    // The new custom claims will propagate to the user's ID token the
    // next time a new one is issued.
  });

// Set admin privilege on the user corresponding to uid.
Map<String, Object> claims = new HashMap<>();
claims.put("admin", true);
FirebaseAuth.getInstance().setCustomUserClaims(uid, claims);
// The new custom claims will propagate to the user's ID token the
// next time a new one is issued.

# Set admin privilege on the user corresponding to uid.
auth.set_custom_user_claims(uid, {'admin': True})
# The new custom claims will propagate to the user's ID token the
# next time a new one is issued.

// Get an auth client from the firebase.App
client, err := app.Auth(ctx)
if err != nil {
	log.Fatalf("error getting Auth client: %v\n", err)
}

// Set admin privilege on the user corresponding to uid.
claims := map[string]interface{}{"admin": true}
err = client.SetCustomUserClaims(ctx, uid, claims)
if err != nil {
	log.Fatalf("error setting custom claims %v\n", err)
}
// The new custom claims will propagate to the user's ID token the
// next time a new one is issued.
auth.go

// Set admin privileges on the user corresponding to uid.
var claims = new Dictionary<string, object>()
{
    { "admin", true },
};
await FirebaseAuth.DefaultInstance.SetCustomUserClaimsAsync(uid, claims);
// The new custom claims will propagate to the user's ID token the
// next time a new one is issued.

自定義聲明對像不應包含任何OIDC保留鍵名稱或Firebase 保留名稱。自定義聲明有效負載不得超過 1000 字節。

發送到後端服務器的 ID 令牌可以使用 Admin SDK 確認用戶的身份和訪問級別，如下所示：

// Verify the ID token first.
getAuth()
  .verifyIdToken(idToken)
  .then((claims) => {
    if (claims.admin === true) {
      // Allow access to requested admin resource.
    }
  });

// Verify the ID token first.
FirebaseToken decoded = FirebaseAuth.getInstance().verifyIdToken(idToken);
if (Boolean.TRUE.equals(decoded.getClaims().get("admin"))) {
  // Allow access to requested admin resource.
}

# Verify the ID token first.
claims = auth.verify_id_token(id_token)
if claims['admin'] is True:
    # Allow access to requested admin resource.
    pass

// Verify the ID token first.
token, err := client.VerifyIDToken(ctx, idToken)
if err != nil {
	log.Fatal(err)
}

claims := token.Claims
if admin, ok := claims["admin"]; ok {
	if admin.(bool) {
		//Allow access to requested admin resource.
	}
}
auth.go

// Verify the ID token first.
FirebaseToken decoded = await FirebaseAuth.DefaultInstance.VerifyIdTokenAsync(idToken);
object isAdmin;
if (decoded.Claims.TryGetValue("admin", out isAdmin))
{
    if ((bool)isAdmin)
    {
        // Allow access to requested admin resource.
    }
}

您還可以檢查用戶現有的自定義聲明，這些聲明可作為用戶對象的屬性使用：

// Lookup the user associated with the specified uid.
getAuth()
  .getUser(uid)
  .then((userRecord) => {
    // The claims can be accessed on the user record.
    console.log(userRecord.customClaims['admin']);
  });

// Lookup the user associated with the specified uid.
UserRecord user = FirebaseAuth.getInstance().getUser(uid);
System.out.println(user.getCustomClaims().get("admin"));

# Lookup the user associated with the specified uid.
user = auth.get_user(uid)
# The claims can be accessed on the user record.
print(user.custom_claims.get('admin'))

// Lookup the user associated with the specified uid.
user, err := client.GetUser(ctx, uid)
if err != nil {
	log.Fatal(err)
}
// The claims can be accessed on the user record.
if admin, ok := user.CustomClaims["admin"]; ok {
	if admin.(bool) {
		log.Println(admin)
	}
}
auth.go

// Lookup the user associated with the specified uid.
UserRecord user = await FirebaseAuth.DefaultInstance.GetUserAsync(uid);
Console.WriteLine(user.CustomClaims["admin"]);

您可以通過為customClaims傳遞 null 來刪除用戶的自定義聲明。

將自定義聲明傳播給客戶端

通過 Admin SDK 在用戶上修改新聲明後，它們會通過 ID 令牌以下列方式傳播到客戶端上經過身份驗證的用戶：

• 修改自定義聲明後，用戶登錄或重新驗證。結果頒發的 ID 令牌將包含最新的聲明。
• 舊令牌過期後，現有用戶會話會刷新其 ID 令牌。
• 通過調用currentUser.getIdToken(true)強制刷新 ID 令牌。

訪問客戶端上的自定義聲明

只能通過用戶的 ID 令牌檢索自定義聲明。根據用戶的角色或訪問級別修改客戶端 UI 可能需要訪問這些聲明。但是，在驗證並解析其聲明後，應始終通過 ID 令牌強制執行後端訪問。自定義聲明不應直接發送到後端，因為它們不能在令牌之外被信任。

最新聲明傳播到用戶的 ID 令牌後，您可以通過檢索 ID 令牌來獲取它們：

firebase.auth().currentUser.getIdTokenResult()
  .then((idTokenResult) => {
     // Confirm the user is an Admin.
     if (!!idTokenResult.claims.admin) {
       // Show admin UI.
       showAdminUI();
     } else {
       // Show regular user UI.
       showRegularUI();
     }
  })
  .catch((error) => {
    console.log(error);
  });

user.getIdToken(false).addOnSuccessListener(new OnSuccessListener<GetTokenResult>() {
  @Override
  public void onSuccess(GetTokenResult result) {
    boolean isAdmin = result.getClaims().get("admin");
    if (isAdmin) {
      // Show admin UI.
      showAdminUI();
    } else {
      // Show regular user UI.
      showRegularUI();
    }
  }
});

user.getIDTokenResult(completion: { (result, error) in
  guard let admin = result?.claims?["admin"] as? NSNumber else {
    // Show regular user UI.
    showRegularUI()
    return
  }
  if admin.boolValue {
    // Show admin UI.
    showAdminUI()
  } else {
    // Show regular user UI.
    showRegularUI()
  }
})

user.getIDTokenResultWithCompletion:^(FIRAuthTokenResult *result,
                                      NSError *error) {
  if (error != nil) {
    BOOL *admin = [result.claims[@"admin"] boolValue];
    if (admin) {
      // Show admin UI.
      [self showAdminUI];
    } else {
      // Show regular user UI.
      [self showRegularUI];
    }
  }
}];

自定義聲明的最佳實踐

自定義聲明僅用於提供訪問控制。它們並非旨在存儲其他數據（例如配置文件和其他自定義數據）。雖然這似乎是一種方便的機制，但強烈建議不要這樣做，因為這些聲明存儲在 ID 令牌中，並且可能導致性能問題，因為所有經過身份驗證的請求始終包含與登錄用戶對應的 Firebase ID 令牌。

• 使用自定義聲明來存儲數據，僅用於控制用戶訪問。所有其他數據應通過實時數據庫或其他服務器端存儲單獨存儲。
• 自定義聲明的大小有限。傳遞大於 1000 字節的自定義聲明有效負載將引發錯誤。

示例和用例

以下示例說明了特定 Firebase 用例上下文中的自定義聲明。

在創建用戶時通過 Firebase 函數定義角色

在此示例中，自定義聲明是在使用 Cloud Functions 創建用戶時設置的。

可以使用 Cloud Functions 添加自定義聲明，並使用實時數據庫立即傳播。該函數僅在使用onCreate觸發器註冊時調用。一旦設置了自定義聲明，它們就會傳播到所有現有和未來的會話。下次用戶使用用戶憑據登錄時，令牌將包含自定義聲明。

客戶端實現 (JavaScript)

const provider = new firebase.auth.GoogleAuthProvider();
firebase.auth().signInWithPopup(provider)
.catch(error => {
  console.log(error);
});

let callback = null;
let metadataRef = null;
firebase.auth().onAuthStateChanged(user => {
  // Remove previous listener.
  if (callback) {
    metadataRef.off('value', callback);
  }
  // On user login add new listener.
  if (user) {
    // Check if refresh is required.
    metadataRef = firebase.database().ref('metadata/' + user.uid + '/refreshTime');
    callback = (snapshot) => {
      // Force refresh to pick up the latest custom claims changes.
      // Note this is always triggered on first call. Further optimization could be
      // added to avoid the initial trigger when the token is issued and already contains
      // the latest claims.
      user.getIdToken(true);
    };
    // Subscribe new listener to changes on that node.
    metadataRef.on('value', callback);
  }
});

雲函數邏輯

添加了一個新的數據庫節點 (metadata/($uid)}，其讀/寫限制為經過身份驗證的用戶。

const functions = require('firebase-functions');
const { initializeApp } = require('firebase-admin/app');
const { getAuth } = require('firebase-admin/auth');
const { getDatabase } = require('firebase-admin/database');

initializeApp();

// On sign up.
exports.processSignUp = functions.auth.user().onCreate(async (user) => {
  // Check if user meets role criteria.
  if (
    user.email &&
    user.email.endsWith('@admin.example.com') &&
    user.emailVerified
  ) {
    const customClaims = {
      admin: true,
      accessLevel: 9
    };

    try {
      // Set custom user claims on this newly created user.
      await getAuth().setCustomUserClaims(user.uid, customClaims);

      // Update real-time database to notify client to force refresh.
      const metadataRef = getDatabase().ref('metadata/' + user.uid);

      // Set the refresh time to the current UTC timestamp.
      // This will be captured on the client to force a token refresh.
      await  metadataRef.set({refreshTime: new Date().getTime()});
    } catch (error) {
      console.log(error);
    }
  }
});

數據庫規則

{
  "rules": {
    "metadata": {
      "$user_id": {
        // Read access only granted to the authenticated user.
        ".read": "$user_id === auth.uid",
        // Write access only via Admin SDK.
        ".write": false
      }
    }
  }
}

通過 HTTP 請求定義角色

以下示例通過 HTTP 請求對新登錄的用戶設置自定義用戶聲明。

客戶端實現 (JavaScript)

const provider = new firebase.auth.GoogleAuthProvider();
firebase.auth().signInWithPopup(provider)
.then((result) => {
  // User is signed in. Get the ID token.
  return result.user.getIdToken();
})
.then((idToken) => {
  // Pass the ID token to the server.
  $.post(
    '/setCustomClaims',
    {
      idToken: idToken
    },
    (data, status) => {
      // This is not required. You could just wait until the token is expired
      // and it proactively refreshes.
      if (status == 'success' && data) {
        const json = JSON.parse(data);
        if (json && json.status == 'success') {
          // Force token refresh. The token claims will contain the additional claims.
          firebase.auth().currentUser.getIdToken(true);
        }
      }
    });
}).catch((error) => {
  console.log(error);
});

後端實施（管理 SDK）

app.post('/setCustomClaims', async (req, res) => {
  // Get the ID token passed.
  const idToken = req.body.idToken;

  // Verify the ID token and decode its payload.
  const claims = await getAuth().verifyIdToken(idToken);

  // Verify user is eligible for additional privileges.
  if (
    typeof claims.email !== 'undefined' &&
    typeof claims.email_verified !== 'undefined' &&
    claims.email_verified &&
    claims.email.endsWith('@admin.example.com')
  ) {
    // Add custom claims for additional privileges.
    await getAuth().setCustomUserClaims(claims.sub, {
      admin: true
    });

    // Tell client to refresh token on user.
    res.end(JSON.stringify({
      status: 'success'
    }));
  } else {
    // Return nothing.
    res.end(JSON.stringify({ status: 'ineligible' }));
  }
});

升級現有用戶的訪問級別時可以使用相同的流程。以免費用戶升級到付費訂閱為例。用戶的 ID 令牌通過 HTTP 請求與支付信息一起發送到後端服務器。成功處理付款後，通過 Admin SDK 將用戶設置為付費訂閱者。成功的 HTTP 響應返回給客戶端以強制刷新令牌。

通過後端腳本定義角色

可以將循環腳本（不是從客戶端啟動）設置為運行以更新用戶自定義聲明：

getAuth()
  .getUserByEmail('user@admin.example.com')
  .then((user) => {
    // Confirm user is verified.
    if (user.emailVerified) {
      // Add custom claims for additional privileges.
      // This will be picked up by the user on token refresh or next sign in on new device.
      return getAuth().setCustomUserClaims(user.uid, {
        admin: true,
      });
    }
  })
  .catch((error) => {
    console.log(error);
  });

UserRecord user = FirebaseAuth.getInstance()
    .getUserByEmail("user@admin.example.com");
// Confirm user is verified.
if (user.isEmailVerified()) {
  Map<String, Object> claims = new HashMap<>();
  claims.put("admin", true);
  FirebaseAuth.getInstance().setCustomUserClaims(user.getUid(), claims);
}

user = auth.get_user_by_email('user@admin.example.com')
# Confirm user is verified
if user.email_verified:
    # Add custom claims for additional privileges.
    # This will be picked up by the user on token refresh or next sign in on new device.
    auth.set_custom_user_claims(user.uid, {
        'admin': True
    })

user, err := client.GetUserByEmail(ctx, "user@admin.example.com")
if err != nil {
	log.Fatal(err)
}
// Confirm user is verified
if user.EmailVerified {
	// Add custom claims for additional privileges.
	// This will be picked up by the user on token refresh or next sign in on new device.
	err := client.SetCustomUserClaims(ctx, user.UID, map[string]interface{}{"admin": true})
	if err != nil {
		log.Fatalf("error setting custom claims %v\n", err)
	}

}
auth.go

UserRecord user = await FirebaseAuth.DefaultInstance
    .GetUserByEmailAsync("user@admin.example.com");
// Confirm user is verified.
if (user.EmailVerified)
{
    var claims = new Dictionary<string, object>()
    {
        { "admin", true },
    };
    await FirebaseAuth.DefaultInstance.SetCustomUserClaimsAsync(user.Uid, claims);
}

自定義聲明也可以通過 Admin SDK 逐步修改：

getAuth()
  .getUserByEmail('user@admin.example.com')
  .then((user) => {
    // Add incremental custom claim without overwriting existing claims.
    const currentCustomClaims = user.customClaims;
    if (currentCustomClaims['admin']) {
      // Add level.
      currentCustomClaims['accessLevel'] = 10;
      // Add custom claims for additional privileges.
      return getAuth().setCustomUserClaims(user.uid, currentCustomClaims);
    }
  })
  .catch((error) => {
    console.log(error);
  });

UserRecord user = FirebaseAuth.getInstance()
    .getUserByEmail("user@admin.example.com");
// Add incremental custom claim without overwriting the existing claims.
Map<String, Object> currentClaims = user.getCustomClaims();
if (Boolean.TRUE.equals(currentClaims.get("admin"))) {
  // Add level.
  currentClaims.put("level", 10);
  // Add custom claims for additional privileges.
  FirebaseAuth.getInstance().setCustomUserClaims(user.getUid(), currentClaims);
}

user = auth.get_user_by_email('user@admin.example.com')
# Add incremental custom claim without overwriting existing claims.
current_custom_claims = user.custom_claims
if current_custom_claims.get('admin'):
    # Add level.
    current_custom_claims['accessLevel'] = 10
    # Add custom claims for additional privileges.
    auth.set_custom_user_claims(user.uid, current_custom_claims)

user, err := client.GetUserByEmail(ctx, "user@admin.example.com")
if err != nil {
	log.Fatal(err)
}
// Add incremental custom claim without overwriting existing claims.
currentCustomClaims := user.CustomClaims
if currentCustomClaims == nil {
	currentCustomClaims = map[string]interface{}{}
}

if _, found := currentCustomClaims["admin"]; found {
	// Add level.
	currentCustomClaims["accessLevel"] = 10
	// Add custom claims for additional privileges.
	err := client.SetCustomUserClaims(ctx, user.UID, currentCustomClaims)
	if err != nil {
		log.Fatalf("error setting custom claims %v\n", err)
	}

}
auth.go

UserRecord user = await FirebaseAuth.DefaultInstance
    .GetUserByEmailAsync("user@admin.example.com");
// Add incremental custom claims without overwriting the existing claims.
object isAdmin;
if (user.CustomClaims.TryGetValue("admin", out isAdmin) && (bool)isAdmin)
{
    var claims = new Dictionary<string, object>(user.CustomClaims);
    // Add level.
    claims["level"] = 10;
    // Add custom claims for additional privileges.
    await FirebaseAuth.DefaultInstance.SetCustomUserClaimsAsync(user.Uid, claims);
}