인증 제공업체의 사용자 인증 정보를 기존 사용자 계정에 연결하면 사용자가 여러 인증 제공업체를 통해 앱에 로그인할 수 있습니다.
사용자가 로그인할 때 어떤 인증 제공업체를 사용하든 동일한 Firebase 사용자 ID로 본인 확인이 가능합니다. 예를 들어 비밀번호로 로그인한 사용자가 Google 계정을 연결하면 나중에 비밀번호와 Google 계정 중 어느 방법으로든 로그인할 수 있습니다. 또는 익명 사용자가 Facebook 계정을 연결하면 나중에 Facebook으로 로그인해서 앱을 계속 사용할 수 있습니다.
다음과 같이 firebase::auth::Credential 객체를 로그인한 사용자의 LinkWithCredential 메서드에 전달합니다.
// Link the new credential to the currently active user.firebase::auth::Usercurrent_user=auth->current_user();firebase::Future<firebase::auth::AuthResult>result=current_user.LinkWithCredential(credential);
사용자 인증 정보가 다른 사용자 계정에 이미 연결되어 있다면 LinkWithCredential 호출이 실패합니다. 이 경우에는 앱에 맞게 계정과 관련 데이터를 병합하는 과정을 처리해야 합니다.
// Gather data for the currently signed in User.firebase::auth::Usercurrent_user=auth->current_user();std::stringcurrent_email=current_user.email();std::stringcurrent_provider_id=current_user.provider_id();std::stringcurrent_display_name=current_user.display_name();std::stringcurrent_photo_url=current_user.photo_url();// Sign in with the new credentials.firebase::Future<firebase::auth::AuthResult>result=auth->SignInAndRetrieveDataWithCredential(credential);// To keep example simple, wait on the current thread until call completes.while(result.status()==firebase::kFutureStatusPending){Wait(100);}// The new User is now active.if(result.error()==firebase::auth::kAuthErrorNone){firebase::auth::User*new_user=*result.result();// Merge new_user with the user in details.// ...(void)new_user;}
LinkWithCredential 호출이 성공하면 사용자가 연결된 인증 제공업체를 사용해 동일한 Firebase 데이터에 액세스할 수 있습니다.
인증 제공업체와 사용자 계정의 연결 해제하기
특정 인증 제공업체와 계정의 연결을 해제할 수 있습니다. 그러면 사용자가 더 이상 해당 제공업체로 로그인할 수 없게 됩니다.
인증 제공업체와 사용자 계정의 연결을 해제하려면 제공업체 ID를 Unlink 메서드에 전달합니다. 사용자 계정에 연결된 인증 제공업체의 ID를 가져오려면 ProviderData를 호출합니다.
// Unlink the sign-in provider from the currently active user.firebase::auth::Usercurrent_user=auth->current_user();firebase::Future<firebase::auth::AuthResult>result=current_user.Unlink(providerId);
[null,null,["최종 업데이트: 2025-08-04(UTC)"],[],[],null,["| **Important** : There is a [known issue](https://github.com/firebase/firebase-js-sdk/issues/7675) that prevents `linkWithCredentials()` from working correctly in some projects. See the issue report for a workaround and the status of a fix.\n\nYou can allow users to sign in to your app using multiple authentication\nproviders by linking auth provider credentials to an existing user account.\nUsers are identifiable by the same Firebase user ID regardless of the\nauthentication provider they used to sign in. For example, a user who signed in\nwith a password can link a Google account and sign in with either method in the\nfuture. Or, an anonymous user can link a Facebook account and then, later, sign\nin with Facebook to continue using your app.\n\nBefore you begin\n\nAdd support for two or more authentication providers (possibly including\nanonymous authentication) to your app.\n\nLink auth provider credentials to a user account\n\nTo link auth provider credentials to an existing user account:\n\n1. Sign in the user using any authentication provider or method.\n2. Complete the sign-in flow for the new authentication provider up to, but not including, calling one of the [`firebase::auth::Auth::SignInWithCredential`](/docs/reference/cpp/class/firebase/auth/auth#signinwithcredential) methods. For example, get the user's Google ID token, Facebook access token, or email and password.\n3. Get a `firebase::auth::Credential` for the new authentication provider:\n\n **Google Sign-In** \n\n ```c++\n firebase::auth::Credential credential =\n firebase::auth::GoogleAuthProvider::GetCredential(google_id_token,\n nullptr);\n ```\n **Facebook Login** \n\n ```c++\n firebase::auth::Credential credential =\n firebase::auth::FacebookAuthProvider::GetCredential(access_token);\n ```\n **Email-password sign-in** \n\n ```c++\n firebase::auth::Credential credential =\n firebase::auth::EmailAuthProvider::GetCredential(email, password);\n ```\n4. Pass the `firebase::auth::Credential` object to the signed-in user's\n `LinkWithCredential` method:\n\n ```c++\n // Link the new credential to the currently active user.\n firebase::auth::User current_user = auth-\u003ecurrent_user();\n firebase::Future\u003cfirebase::auth::AuthResult\u003e result =\n current_user.LinkWithCredential(credential);\n ```\n\n The call to `LinkWithCredential` will fail if the credentials are\n already linked to another user account. In this situation, you must handle\n merging the accounts and associated data as appropriate for your app: \n\n ```c++\n // Gather data for the currently signed in User.\n firebase::auth::User current_user = auth-\u003ecurrent_user();\n std::string current_email = current_user.email();\n std::string current_provider_id = current_user.provider_id();\n std::string current_display_name = current_user.display_name();\n std::string current_photo_url = current_user.photo_url();\n\n // Sign in with the new credentials.\n firebase::Future\u003cfirebase::auth::AuthResult\u003e result =\n auth-\u003eSignInAndRetrieveDataWithCredential(credential);\n\n // To keep example simple, wait on the current thread until call completes.\n while (result.status() == firebase::kFutureStatusPending) {\n Wait(100);\n }\n\n // The new User is now active.\n if (result.error() == firebase::auth::kAuthErrorNone) {\n firebase::auth::User* new_user = *result.result();\n\n // Merge new_user with the user in details.\n // ...\n (void)new_user;\n }\n ```\n\nIf the call to `LinkWithCredential` succeeds, the user can now sign in using\nany linked authentication provider and access the same Firebase data.\n\nUnlink an auth provider from a user account\n\nYou can unlink an auth provider from an account, so that the user can no\nlonger sign in with that provider.\n\nTo unlink an auth provider from a user account, pass the provider ID to the\n`Unlink` method. You can get the provider IDs of the auth providers\nlinked to a user by calling [`ProviderData`](/docs/reference/cpp/class/firebase/auth/user#providerdata). \n\n```c++\n// Unlink the sign-in provider from the currently active user.\nfirebase::auth::User current_user = auth-\u003ecurrent_user();\nfirebase::Future\u003cfirebase::auth::AuthResult\u003e result =\n current_user.Unlink(providerId);\n```"]]
