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 federated auth provider credentials to a user account
To link credentials from an auth provider such as Google or Facebook to an existing user account:
- Sign in the user using any authentication provider or method.
- Get the
AuthProviderobject that corresponds to the provider you want to link to the user's account. Examples:Web
import { GoogleAuthProvider , FacebookAuthProvider , TwitterAuthProvider , GithubAuthProvider } from "firebase/auth" ; const googleProvider = new GoogleAuthProvider (); const facebookProvider = new FacebookAuthProvider (); const twitterProvider = new TwitterAuthProvider (); const githubProvider = new GithubAuthProvider ();
Web
var googleProvider = new firebase . auth . GoogleAuthProvider (); var facebookProvider = new firebase . auth . FacebookAuthProvider (); var twitterProvider = new firebase . auth . TwitterAuthProvider (); var githubProvider = new firebase . auth . GithubAuthProvider ();
- Prompt the user to sign in with the provider you want to link. You can
prompt your users to sign in either by opening a pop-up window or by
redirecting to the provider's sign-in page. The redirect method is preferred
on mobile devices.
- To sign in with a pop-up window, call
linkWithPopup:Web
import { getAuth , linkWithPopup , GoogleAuthProvider } from "firebase/auth" ; const provider = new GoogleAuthProvider (); const auth = getAuth (); linkWithPopup ( auth . currentUser , provider ). then (( result ) = > { // Accounts successfully linked. const credential = GoogleAuthProvider . credentialFromResult ( result ); const user = result . user ; // ... }). catch (( error ) = > { // Handle Errors here. // ... });
Web
auth . currentUser . linkWithPopup ( provider ). then (( result ) = > { // Accounts successfully linked. var credential = result . credential ; var user = result . user ; // ... }). catch (( error ) = > { // Handle Errors here. // ... });
- To sign in by redirecting to the provider's sign-in page, call
linkWithRedirect: Follow the best practices when using `linkWithRedirect`.After the user signs in, they are redirected back to your page. Then, you can retrieve the sign-in result by callingWeb
import { getAuth , linkWithRedirect , GoogleAuthProvider } from "firebase/auth" ; const provider = new GoogleAuthProvider (); const auth = getAuth (); linkWithRedirect ( auth . currentUser , provider ) . then ( /* ... */ ) . catch ( /* ... */ );
Web
auth . currentUser . linkWithRedirect ( provider ) . then ( /* ... */ ) . catch ( /* ... */ );
getRedirectResultwhen your page loads:Web
import { getRedirectResult } from "firebase/auth" ; getRedirectResult ( auth ). then (( result ) = > { const credential = GoogleAuthProvider . credentialFromResult ( result ); if ( credential ) { // Accounts successfully linked. const user = result . user ; // ... } }). catch (( error ) = > { // Handle Errors here. // ... });
Web
auth . getRedirectResult (). then (( result ) = > { if ( result . credential ) { // Accounts successfully linked. var credential = result . credential ; var user = result . user ; // ... } }). catch (( error ) = > { // Handle Errors here. // ... });
Account linking will 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:
Web
import { getAuth , signInWithCredential , linkWithCredential , OAuthProvider } from "firebase/auth" ; // The implementation of how you store your user data depends on your application const repo = new MyUserDataRepo (); // Get reference to the currently signed-in user const auth = getAuth (); const prevUser = auth . currentUser ; // Get the data which you will want to merge. This should be done now // while the app is still signed in as this user. const prevUserData = repo . get ( prevUser ); // Delete the user's data now, we will restore it if the merge fails repo . delete ( prevUser ); // Sign in user with the account you want to link to signInWithCredential ( auth , newCredential ). then (( result ) = > { console . log ( "Sign In Success" , result ); const currentUser = result . user ; const currentUserData = repo . get ( currentUser ); // Merge prevUser and currentUser data stored in Firebase. // Note: How you handle this is specific to your application const mergedData = repo . merge ( prevUserData , currentUserData ); const credential = OAuthProvider . credentialFromResult ( result ); return linkWithCredential ( prevUser , credential ) . then (( linkResult ) = > { // Sign in with the newly linked credential const linkCredential = OAuthProvider . credentialFromResult ( linkResult ); return signInWithCredential ( auth , linkCredential ); }) . then (( signInResult ) = > { // Save the merged data to the new user repo . set ( signInResult . user , mergedData ); }); }). catch (( error ) = > { // If there are errors we want to undo the data merge/deletion console . log ( "Sign In Error" , error ); repo . set ( prevUser , prevUserData ); });
Web
// The implementation of how you store your user data depends on your application var repo = new MyUserDataRepo (); // Get reference to the currently signed-in user var prevUser = auth . currentUser ; // Get the data which you will want to merge. This should be done now // while the app is still signed in as this user. var prevUserData = repo . get ( prevUser ); // Delete the user's data now, we will restore it if the merge fails repo . delete ( prevUser ); // Sign in user with the account you want to link to auth . signInWithCredential ( newCredential ). then (( result ) = > { console . log ( "Sign In Success" , result ); var currentUser = result . user ; var currentUserData = repo . get ( currentUser ); // Merge prevUser and currentUser data stored in Firebase. // Note: How you handle this is specific to your application var mergedData = repo . merge ( prevUserData , currentUserData ); return prevUser . linkWithCredential ( result . credential ) . then (( linkResult ) = > { // Sign in with the newly linked credential return auth . signInWithCredential ( linkResult . credential ); }) . then (( signInResult ) = > { // Save the merged data to the new user repo . set ( signInResult . user , mergedData ); }); }). catch (( error ) = > { // If there are errors we want to undo the data merge/deletion console . log ( "Sign In Error" , error ); repo . set ( prevUser , prevUserData ); });
- To sign in with a pop-up window, call
Link email address and password credentials to a user account
To add email address and password credentials to an existing user account:
- Sign in the user using any authentication provider or method.
- Prompt the user for an email address and new password.
- Create an
AuthCredentialobject with the email address and password:Web
import { EmailAuthProvider } from "firebase/auth" ; const credential = EmailAuthProvider . credential ( email , password );
Web
var credential = firebase . auth . EmailAuthProvider . credential ( email , password );
-
Pass the
AuthCredentialobject to the signed-in user'slinkWithCredentialmethod:Web
import { getAuth , linkWithCredential } from "firebase/auth" ; const auth = getAuth (); linkWithCredential ( auth . currentUser , credential ) . then (( usercred ) = > { const user = usercred . user ; console . log ( "Account linking success" , user ); }). catch (( error ) = > { console . log ( "Account linking error" , error ); });
Web
auth . currentUser . linkWithCredential ( credential ) . then (( usercred ) = > { var user = usercred . user ; console . log ( "Account linking success" , user ); }). catch (( error ) = > { console . log ( "Account linking error" , error ); });
The call to
linkWithCredentialwill 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 (see example above).
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 the unlink
method. You can get the provider IDs of the auth providers
linked to a user from the providerData
property.
Web
import { getAuth , unlink } from "firebase/auth" ; const auth = getAuth (); unlink ( auth . currentUser , providerId ). then (() = > { // Auth provider unlinked from account // ... }). catch (( error ) = > { // An error happened // ... });
Web
user . unlink ( providerId ). then (() = > { // Auth provider unlinked from account // ... }). catch (( error ) = > { // An error happened // ... });
Troubleshooting
If you encounter errors when trying to link multiple accounts, see the documentation on verified email addresses .
