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.
시작하기 전에
앱에 2개 이상의 인증 제공업체(익명 인증 포함)에 대한 지원을 추가하세요.
사용자 계정에 인증 제공업체의 사용자 인증 정보 연결하기
다음과 같이 기존 사용자 계정에 인증 제공업체의 사용자 인증 정보를 연결합니다.
인증 제공업체 또는 인증 방법을 사용해 사용자를 로그인 처리합니다.
새로운 인증 제공업체의 로그인 과정을 진행하되 FirebaseAuth.signInWith 메서드 호출 전까지만 진행합니다. 예를 들면 사용자의 Google ID 토큰, Facebook 액세스 토큰, 또는 이메일 주소와 비밀번호를 가져옵니다.
FirebaseUserprevUser=FirebaseAuth.getInstance().getCurrentUser();mAuth.signInWithCredential(credential).addOnCompleteListener(newOnCompleteListener<AuthResult>(){@OverridepublicvoidonComplete(@NonNullTask<AuthResult>task){FirebaseUsercurrentUser=task.getResult().getUser();// Merge prevUser and currentUser accounts and data// ...}});
[null,null,["최종 업데이트: 2025-08-21(UTC)"],[],[],null,["# Link Multiple Auth Providers to an Account on Android\n\n| **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----------------\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------------------------------------------------\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 [`FirebaseAuth.signInWith`](/docs/reference/android/com/google/firebase/auth/FirebaseAuth#public-method-summary) methods. For example, get the user's Google ID token, Facebook access token, or email and password.\n3. Get a `AuthCredential` for the new authentication provider:\n\n ##### Google Sign-In\n\n ### Kotlin\n\n ```kotlin\n val credential = GoogleAuthProvider.getCredential(googleIdToken, null)https://github.com/firebase/snippets-android/blob/391c1646eacf44d2aab3f76bcfa60dfc6c14acf1/auth/app/src/main/java/com/google/firebase/quickstart/auth/kotlin/MainActivity.kt#L394-L394\n ```\n\n ### Java\n\n ```java\n AuthCredential credential = GoogleAuthProvider.getCredential(googleIdToken, null);https://github.com/firebase/snippets-android/blob/391c1646eacf44d2aab3f76bcfa60dfc6c14acf1/auth/app/src/main/java/com/google/firebase/quickstart/auth/MainActivity.java#L479-L479\n ```\n\n ##### Facebook Login\n\n ### Kotlin\n\n ```kotlin\n val credential = FacebookAuthProvider.getCredential(token.token)https://github.com/firebase/snippets-android/blob/391c1646eacf44d2aab3f76bcfa60dfc6c14acf1/auth/app/src/main/java/com/google/firebase/quickstart/auth/kotlin/MainActivity.kt#L401-L401\n ```\n\n ### Java\n\n ```java\n AuthCredential credential = FacebookAuthProvider.getCredential(token.getToken());https://github.com/firebase/snippets-android/blob/391c1646eacf44d2aab3f76bcfa60dfc6c14acf1/auth/app/src/main/java/com/google/firebase/quickstart/auth/MainActivity.java#L487-L487\n ```\n\n ##### Email-password sign-in\n\n ### Kotlin\n\n ```kotlin\n val credential = EmailAuthProvider.getCredential(email, password)https://github.com/firebase/snippets-android/blob/391c1646eacf44d2aab3f76bcfa60dfc6c14acf1/auth/app/src/main/java/com/google/firebase/quickstart/auth/kotlin/MainActivity.kt#L409-L409\n ```\n\n ### Java\n\n ```java\n AuthCredential credential = EmailAuthProvider.getCredential(email, password);https://github.com/firebase/snippets-android/blob/391c1646eacf44d2aab3f76bcfa60dfc6c14acf1/auth/app/src/main/java/com/google/firebase/quickstart/auth/MainActivity.java#L495-L495\n ```\n4. Pass the `AuthCredential` object to the signed-in user's\n `linkWithCredential` method:\n\n ### Kotlin\n\n ```kotlin\n auth.currentUser!!.linkWithCredential(credential)\n .addOnCompleteListener(this) { task -\u003e\n if (task.isSuccessful) {\n Log.d(TAG, \"linkWithCredential:success\")\n val user = task.result?.user\n updateUI(user)\n } else {\n Log.w(TAG, \"linkWithCredential:failure\", task.exception)\n Toast.makeText(\n baseContext,\n \"Authentication failed.\",\n Toast.LENGTH_SHORT,\n ).show()\n updateUI(null)\n }\n }https://github.com/firebase/snippets-android/blob/391c1646eacf44d2aab3f76bcfa60dfc6c14acf1/auth/app/src/main/java/com/google/firebase/quickstart/auth/kotlin/AnonymousAuthActivity.kt#L66-L81\n ```\n\n ### Java\n\n ```java\n mAuth.getCurrentUser().linkWithCredential(credential)\n .addOnCompleteListener(this, new OnCompleteListener\u003cAuthResult\u003e() {\n @Override\n public void onComplete(@NonNull Task\u003cAuthResult\u003e task) {\n if (task.isSuccessful()) {\n Log.d(TAG, \"linkWithCredential:success\");\n FirebaseUser user = task.getResult().getUser();\n updateUI(user);\n } else {\n Log.w(TAG, \"linkWithCredential:failure\", task.getException());\n Toast.makeText(AnonymousAuthActivity.this, \"Authentication failed.\",\n Toast.LENGTH_SHORT).show();\n updateUI(null);\n }\n }\n });https://github.com/firebase/snippets-android/blob/391c1646eacf44d2aab3f76bcfa60dfc6c14acf1/auth/app/src/main/java/com/google/firebase/quickstart/auth/AnonymousAuthActivity.java#L91-L106\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 ### Kotlin\n\n ```kotlin\n val prevUser = auth.currentUser\n auth.signInWithCredential(credential)\n .addOnSuccessListener { result -\u003e\n val currentUser = result.user\n // Merge prevUser and currentUser accounts and data\n // ...\n }\n .addOnFailureListener {\n // ...\n }https://github.com/firebase/snippets-android/blob/391c1646eacf44d2aab3f76bcfa60dfc6c14acf1/auth/app/src/main/java/com/google/firebase/quickstart/auth/kotlin/MainActivity.kt#L250-L259\n ```\n\n ### Java\n\n ```java\n FirebaseUser prevUser = FirebaseAuth.getInstance().getCurrentUser();\n mAuth.signInWithCredential(credential)\n .addOnCompleteListener(new OnCompleteListener\u003cAuthResult\u003e() {\n @Override\n public void onComplete(@NonNull Task\u003cAuthResult\u003e task) {\n FirebaseUser currentUser = task.getResult().getUser();\n // Merge prevUser and currentUser accounts and data\n // ...\n }\n });https://github.com/firebase/snippets-android/blob/391c1646eacf44d2aab3f76bcfa60dfc6c14acf1/auth/app/src/main/java/com/google/firebase/quickstart/auth/MainActivity.java#L303-L312\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-------------------------------------------\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 [`getProviderData`](/docs/reference/android/com/google/firebase/auth/FirebaseUser#getProviderData()). \n\n### Kotlin\n\n```kotlin\nFirebase.auth.currentUser!!.unlink(providerId)\n .addOnCompleteListener(this) { task -\u003e\n if (task.isSuccessful) {\n // Auth provider unlinked from account\n // ...\n }\n }https://github.com/firebase/snippets-android/blob/391c1646eacf44d2aab3f76bcfa60dfc6c14acf1/auth/app/src/main/java/com/google/firebase/quickstart/auth/kotlin/MainActivity.kt#L265-L271\n```\n\n### Java\n\n```java\nmAuth.getCurrentUser().unlink(providerId)\n .addOnCompleteListener(this, new OnCompleteListener\u003cAuthResult\u003e() {\n @Override\n public void onComplete(@NonNull Task\u003cAuthResult\u003e task) {\n if (task.isSuccessful()) {\n // Auth provider unlinked from account\n // ...\n }\n }\n });https://github.com/firebase/snippets-android/blob/391c1646eacf44d2aab3f76bcfa60dfc6c14acf1/auth/app/src/main/java/com/google/firebase/quickstart/auth/MainActivity.java#L321-L330\n```"]]
