Link Multiple Auth Providers to an Account using C++
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You can allow users to sign in to your app using multiple authentication
providers by linking auth provider credentials to an existing user account.
Users are identifiable by the same Firebase user ID regardless of the
authentication provider they used to sign in. For example, a user who signed in
with a password can link a Google account and sign in with either method in the
future. Or, an anonymous user can link a Facebook account and then, later, sign
in with Facebook to continue using your app.
Before you begin
Add support for two or more authentication providers (possibly including
anonymous authentication) to your app.
Link auth provider credentials to a user account
To link auth provider credentials to an existing user account:
Sign in the user using any authentication provider or method.
Complete the sign-in flow for the new authentication provider up to, but not
including, calling one of thefirebase::auth::Auth::SignInWithCredentialmethods. For example, get
the user's Google ID token, Facebook access token, or email and password.
Get afirebase::auth::Credentialfor the new authentication provider:
Pass thefirebase::auth::Credentialobject to the signed-in user'sLinkWithCredentialmethod:
// 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);
The call toLinkWithCredentialwill fail if the credentials are
already linked to another user account. In this situation, you must handle
merging the accounts and associated data as appropriate for your app:
// 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;}
If the call toLinkWithCredentialsucceeds, the user can now sign in using
any linked authentication provider and access the same Firebase data.
Unlink an auth provider from a user account
You can unlink an auth provider from an account, so that the user can no
longer sign in with that provider.
To unlink an auth provider from a user account, pass the provider ID to theUnlinkmethod. You can get the provider IDs of the auth providers
linked to a user by callingProviderData.
// 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);
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Missing the information I need","missingTheInformationINeed","thumb-down"],["Too complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-09-05 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```\n\nTroubleshooting\n\nIf you encounter errors when trying to link multiple accounts, see the\n[documentation on\nverified email addresses](https://firebase.google.com/docs/auth/users#verified_email_addresses)."]]
