# FirebaseUI for Auth

FirebaseUI is an open-source library that offers simple,
customizable UI bindings on top of the core
[Firebase](https://firebase.google.com) SDKs. It aims to eliminate boilerplate
code and promote best practices (both user experience and security) for
authentication.

A simple API is provided for drop-in user authentication which handles the flow
of signing in users with email addresses and passwords, phone numbers, and federated identity
providers such as Google Sign-In, and Facebook Login. It is built on top of
[Firebase Auth](https://firebase.google.com/docs/auth).

The best practices embodied in FirebaseUI aim to maximize sign-in
and sign-up conversion for your app. It integrates with
[Smart Lock for Passwords](https://developers.google.com/identity/smartlock-passwords/android/)
to store and retrieve credentials, enabling automatic and single-tap sign-in to
your app for returning users. It also handles tricky use cases like
account recovery and account linking that are security sensitive and
difficult to implement correctly using the base APIs provided by Firebase Auth.

FirebaseUI auth can be easily customized to fit with the rest of your app's
visual style. As it is open source, you are also free to modify it to exactly
fit your preferred user experience.

Equivalent FirebaseUI auth libraries are also available for
[iOS](https://github.com/firebase/firebaseui-ios/)
and [Web](https://github.com/firebase/firebaseui-web/).

## Table of contents

1. [Demo](#demo)
1. [Configuration](#configuration)
   1. [Basics](#basics)
   1. [Themes](#themes)
   1. [Provider config](#identity-provider-configuration)
   1. [Auth emulator config](#auth-emulator-configuration)
1. [Usage instructions](#using-firebaseui-for-authentication)
   1. [AuthUI sign-in](#authui-sign-in)
   1. [Handling responses](#handling-the-sign-in-response)
   1. [Silent sign-in](#silent-sign-in)
   1. [Sign out](#sign-out)
   1. [Account deletion](#deleting-accounts)
   1. [Upgrading Anonymous Users](#upgrading-anonymous-users)
1. [UI Customization](#ui-customization)
   1. [Custom layout](#custom-layout)
   1. [Strings](#strings)
1. [OAuth scopes](#oauth-scope-customization)
   1. [Google](#google-1)
   1. [Facebook](#facebook-1)
   1. [Twitter](#twitter-1)

## Demo

![FirebaseUI authentication demo on Android](demo.gif)

## Configuration

As a pre-requisite, ensure your application is configured for use with
Firebase: see the
[Firebase documentation](https://firebase.google.com/docs/android/setup).
Then, add the FirebaseUI auth library dependency. If your project uses
Gradle, add the dependency:

```groovy
dependencies {
    // ...
    implementation 'com.firebaseui:firebase-ui-auth:8.0.2'

    // Required only if Facebook login support is required
    // Find the latest Facebook SDK releases here: https://github.com/facebook/facebook-android-sdk/blob/master/CHANGELOG.md
    implementation 'com.facebook.android:facebook-login:8.1.0'
}
```

FirebaseUI includes translations for all string resources. In order to
ensure that you only get the translations relevant to your application, we recommend changing the
`resConfigs` of your application module:

```groovy
android {
    // ...

    defaultConfig {
       // ...
       resConfigs "en" // And any other languages you support
    }
}
```

See the [Android documentation](https://developer.android.com/studio/build/shrink-code.html#unused-alt-resources)
for more information.

### Basics

There are three main steps to adding FirebaseUI in your app:

  1. Build a sign in `Intent` using `AuthUI#createSignInIntentBuilder()`
  2. Launch the `Intent` using an `ActivityResultLauncher`
  3. Handle the result.
  
```java
private ActivityResultLauncher<Intent> signInLauncher = registerForActivityResult(
  new FirebaseAuthUIActivityResultContract(),
  (result) -> {
    // Handle the FirebaseAuthUIAuthenticationResult
    // ...                
  });

// ... 

private void startSignIn() {
  Intent signInIntent = AuthUI.getInstance()
      .createSignInIntentBuilder()
      // ... options ...
      .build();

  signInLauncher.launch(signInIntent);
}
```

### Themes

As of version `8.0.0` FirebaseUI uses Material Design Components and themes. To use FirebaseUI seamlessly in your app you should provide a theme resource which provides Material Design color attributes ([read more here](https://material.io/blog/android-material-theme-color)).

At a minimum your theme should define the following attributes:

  * `colorPrimary`
  * `colorPrimaryVariant`
  * `colorAccent`
  * `android:statusBarColor` (API > 21) or `colorPrimaryDark` (API < 21)

#### Using your app theme

To configure FirebaseUI to match your app's exising theme, simply pass your main theme attribute to `setTheme()`:

This would then be used in the construction of the sign-in intent:

```java
Intent signInIntent = 
    AuthUI.getInstance(this).createSignInIntentBuilder()
        // ...
        .setTheme(R.style.AppTheme)
        .build())
```

#### Using a custom theme

For example, here is a simple green sign-in theme:

```xml
<style name="GreenTheme" parent="FirebaseUI">
    <item name="colorPrimary">@color/material_green_500</item>
    <item name="colorPrimaryVariant">@color/material_green_700</item>
    <item name="colorAccent">@color/material_purple_a700</item>
    <item name="android:colorBackground">@color/material_green_50</item>

    <!-- On API 21+ you can use android:statusBarColor -->
    <item name="colorPrimaryDark">@color/material_green_700</item>
</style>
```

With associated colors:

```xml
<color name="material_green_50">#E8F5E9</color>
<color name="material_green_500">#4CAF50</color>
<color name="material_green_700">#388E3C</color>
<color name="material_purple_a700">#AA00FF</color>
```

This would then be used in the construction of the sign-in intent:

```java
Intent signinIntent =
    AuthUI.getInstance(this).createSignInIntentBuilder()
        // ...
        .setTheme(R.style.GreenTheme)
        .build();
```

### Identity provider configuration

In order to use either Google, Facebook, Twitter, Microsoft, Apple, GitHub or Yahoo accounts with
your app, ensure that these authentication methods are first configured in the Firebase console.

#### Google

FirebaseUI client-side configuration for Google sign-in is then provided
automatically by the
[google-services gradle plugin](https://developers.google.com/android/guides/google-services-plugin).

#### Facebook

If support for Facebook Login is also required, define the
resource string `facebook_application_id` to match the application ID in
the [Facebook developer dashboard](https://developers.facebook.com):

```xml
<resources>
    <!-- ... -->
    <string name="facebook_application_id" translatable="false">APP_ID</string>
    <!-- Facebook Application ID, prefixed by 'fb'. Enables Chrome Custom tabs. -->
    <string name="facebook_login_protocol_scheme" translatable="false">fbAPP_ID</string>
</resources>
```

#### Microsoft, Apple, Twitter, GitHub and Yahoo

No FirebaseUI configuration is required for these providers.

We support the use of scopes and custom parameters for these providers. For example:

```java
List<String> scopes =
    new ArrayList<String>() {
      {
        add("mail.read");
        add("calendars.read");
      }
    };

Map<String, String> customParams = new HashMap<>();
customParams.put("tenant", "TENANT_ID");

IdpConfig microsoftConfig = new IdpConfig.MicrosoftBuilder()
                    .setScopes(scopes)
                    .setCustomParameters(customParams)
                    .build();
selectedProviders.add(microsoftConfig);
```

Note: unlike other sign-in methods, signing in with these providers involves the use of a
[Custom Chrome Tab](https://developer.chrome.com/multidevice/android/customtabs).

##### Twitter

You must enable the "Request email addresses from users" permission in the "Permissions" tab of your
Twitter app.

### Auth emulator configuration

As of version `7.0.0` FirebaseUI is compatible with the Firebase Authentication emulator:
https://firebase.google.com/docs/emulator-suite

Use the `useEmulator` method to point an AuthUI instance at the emulator:

```java
AuthUI authUI = AuthUI.getInstance();

// "10.0.2.2" is the special host value for contacting "localhost" from within
// the Android Emulator
authUI.useEmulator("10.0.2.2", 9099);
```

By default Android blocks connections to `http://` endpoints such as the Auth emulator.
To allow your app to communicate with the Auth emulator, use a [network security configuration](https://developer.android.com/training/articles/security-config)
or set `android:usesCleartextTraffic="true"` in `AndroidManifest.xml`.

## Using FirebaseUI for authentication

Before invoking the FirebaseUI authentication flow, your app should check
whether a
[user is already signed in](https://firebase.google.com/docs/auth/android/manage-users#get_the_currently_signed-in_user)
from a previous session:

```java
FirebaseAuth auth = FirebaseAuth.getInstance();
if (auth.getCurrentUser() != null) {
    // already signed in
} else {
    // not signed in
}
```

The entry point to the authentication flow is the
`com.firebase.ui.auth.AuthUI` class.
If your application uses the default `FirebaseApp` instance, an AuthUI
instance can be retrieved simply by calling `AuthUI.getInstance()`.
If an alternative app instance is required, call
`AuthUI.getInstance(app)` instead, passing the appropriate `FirebaseApp`
instance.

### AuthUI sign-in

If a user is not currently signed in, as can be determined by checking
`auth.getCurrentUser() != null` (where `auth` is the `FirebaseAuth` instance
associated with your `FirebaseApp`), then the sign-in process can be started by
creating a sign-in intent using `AuthUI.SignInIntentBuilder`. A builder instance
can be retrieved by calling `createSignInIntentBuilder()` on the retrieved
AuthUI instance.

The builder provides the following customization options for the authentication flow:

* The set of authentication providers can be specified.
* The terms of service URL for your app can be specified, which is included as
  a link in the small-print of the account creation step for new users. If no
  terms of service URL is provided, the associated small-print is omitted.
* A custom theme can be specified for the flow, which is applied to all the
  activities in the flow for consistent colors and typography.

#### Sign-in examples

If no customization is required, and only email authentication is required, the sign-in flow
can be started as follows:

```java
// Get an instance of AuthUI based on the default app
Intent signInIntent =
    AuthUI.getInstance().createSignInIntentBuilder().build();

signInLauncher.launch(signInIntent);
```

To kick off the FirebaseUI sign in flow, use an `ActivityResultLauncher` to launch the Intent you built.
See the [response codes](#response-codes) section below for more details on receiving the results of the sign in flow.

##### Adding providers

You can enable sign-in providers like Google Sign-In or Facebook Log In by calling the
`setAvailableProviders` method:

```java
Intent signInIntent =
        AuthUI.getInstance()
                .createSignInIntentBuilder()
                .setAvailableProviders(Arrays.asList(
                        new AuthUI.IdpConfig.GoogleBuilder().build(),
                        new AuthUI.IdpConfig.FacebookBuilder().build(),
                        new AuthUI.IdpConfig.TwitterBuilder().build(),
                        new AuthUI.IdpConfig.MicrosoftBuilder().build(),
                        new AuthUI.IdpConfig.YahooBuilder().build(),
                        new AuthUI.IdpConfig.AppleBuilder().build(),
                        new AuthUI.IdpConfig.EmailBuilder().build(),
                        new AuthUI.IdpConfig.PhoneBuilder().build(),
                        new AuthUI.IdpConfig.AnonymousBuilder().build()))
                .build();
```

##### Configuring Email Link Sign In

To use email link sign in, you will first need to enable it in the Firebase Console. Additionally, you will
also have to enable Firebase Dynamic Links.

You can enable email link sign in by calling the `enableEmailLinkSignIn` on an `EmailBuilder` instance. You will also need
to provide a valid `ActionCodeSettings` object with `setHandleCodeInApp` set to true. Additionally, you need to allowlist the
URL you pass to `setUrl`; you can do so in the Firebase Console (Authentication -> Sign in Methods -> Authorized domains).

```java

ActionCodeSettings actionCodeSettings = ActionCodeSettings.newBuilder()
        .setAndroidPackageName(/*yourPackageName*/, /*installIfNotAvailable*/true, /*minimumVersion*/null)
        .setHandleCodeInApp(true)
        .setUrl("https://google.com") // This URL needs to be allowlisted
        .build();

Intent signInIntent =
        AuthUI.getInstance()
                .createSignInIntentBuilder()
                .setAvailableProviders(Arrays.asList(
                        new AuthUI.IdpConfig.EmailBuilder().enableEmailLinkSignIn()
                        .setActionCodeSettings(actionCodeSettings).build())
                .build();
```

If you want to catch the link in a specific activity, please follow the steps outlined [here](https://firebase.google.com/docs/auth/android/email-link-auth).
Otherwise, the link will redirect to your launcher activity.

Once you catch the deep link, you will need to call verify that we can handle it for you. If we can, you need to then
pass it to us via `setEmailLink`.

```java
if (AuthUI.canHandleIntent(getIntent())) {
   if (getIntent().getExtras() == null) {
         return;
   }
   String link = getIntent().getData().toString();
   if (link != null) {
      Intent signInIntent =
              AuthUI.getInstance()
                      .createSignInIntentBuilder()
                      .setEmailLink(link)
                      .setAvailableProviders(getAvailableProviders())
                      .build();
      signInLauncher.launch(signInIntent);
   }
}
```

#### Cross device support

We support cross device email link sign in for the normal flows. It is not supported with anonymous user upgrade. By default,
cross device support is enabled. You can disable it by calling `setForceSameDevice` on the `EmailBuilder` instance.

##### Adding a ToS and privacy policy

A terms of service URL and privacy policy URL are generally required:

```java
Intent signInIntent =
    AuthUI.getInstance()
        .createSignInIntentBuilder()
        .setAvailableProviders(...)
        .setTosAndPrivacyPolicyUrls("https://superapp.example.com/terms-of-service.html",
                                    "https://superapp.example.com/privacy-policy.html")
        .build();
```

##### Smart Lock

By default, FirebaseUI uses [Smart Lock for Passwords](https://developers.google.com/identity/smartlock-passwords/android/)
to store the user's credentials and automatically sign users into your app on subsequent attempts.
Using Smart Lock is recommended to provide the best user experience, but in some cases you may want
to disable Smart Lock for testing or development. To disable Smart Lock, you can use the
`setIsSmartLockEnabled` method when building your sign-in Intent:

```java
Intent signInIntent =
    AuthUI.getInstance()
        .createSignInIntentBuilder()
        .setIsSmartLockEnabled(false)
        .build();
```

###### Smart Lock hints

If you'd like to keep Smart Lock's "hints" but disable the saving/retrieving of credentials, then
you can use the two-argument version of `setIsSmartLockEnabled`:

```java
Intent signInIntent =
    AuthUI.getInstance()
        .createSignInIntentBuilder()
        .setIsSmartLockEnabled(false, true)
        .build();
```

###### Smart Lock in dev builds

It is often desirable to disable Smart Lock in development but enable it in production. To achieve
this, you can use the `BuildConfig.DEBUG` flag to control Smart Lock:

```java
Intent signInIntent =
    AuthUI.getInstance()
        .createSignInIntentBuilder()
        .setIsSmartLockEnabled(!BuildConfig.DEBUG /* credentials */, true /* hints */)
        .build();
```

##### Phone number authentication customization

###### Setting a default phone number
When using the phone verification provider and the number is known in advance, it is possible to
provide a default phone number (in international format) that will be used to prepopulate the
country code and phone number input fields. The user is still able to edit the number if desired.

```java
IdpConfig phoneConfigWithDefaultNumber = new IdpConfig.PhoneBuilder()
        .setDefaultNumber("+123456789")
        .build();
```

Alternatively, you can set the default country (alpha-2 format) to be shown in the country selector.

```java
IdpConfig phoneConfigWithDefaultNumber = new IdpConfig.PhoneBuilder()
        .setDefaultCountryIso("ca")
        .build();
```

It is also possible to set a default country code along with a national number if a specific country
is your app's target audience. This will take precedence over the full default phone number if both
are provided.

```java
IdpConfig phoneConfigWithDefaultNumber = new IdpConfig.PhoneBuilder()
        .setDefaultNumber("ca", "23456789")
        .build();
```

###### Limiting the list of available countries in the country selector

You can limit the countries shown in the country selector list. By default, all countries are shown.

You can provide a list of countries to allowlist or blocklist. You can populate these lists with
ISO (alpha-2) and E164 formatted country codes.

```java
List<String> allowedCountries = new ArrayList<String>();
allowedCountries.add("+1");
allowedCountries.add("gr");

IdpConfig phoneConfigWithAllowedCountries = new IdpConfig.PhoneBuilder()
        .setAllowedCountries(allowedCountries)
        .build();
```
All countries with the country code +1 will be present in the selector as well as Greece ('gr').

You may want to exclude a few countries from the list and avoid creating a allowlist with
many countries. You can instead provide a list of countries to blocklist. By doing so, all countries
excluding the ones you provide will be in the selector.

```java
List<String> blockedCountries = new ArrayList<String>();
blockedCountries.add("+1");
blockedCountries.add("gr");

IdpConfig phoneConfigWithBlockedCountries = new IdpConfig.PhoneBuilder()
        .setBlockedCountries(blockedCountries)
        .build();
```

The country code selector will exclude all countries with a country code of +1 and Greece ('gr').

Note: You can't provide both a list of countries to allowlist and blocklist. If you do, a runtime
exception will be thrown.

This change is purely UI based. We do not restrict users from signing in with their phone number.
They will simply be unable to choose their country in the selector, but there may be another country
sharing the same country code (e.g. US and CA are +1).

#####

### Handling the sign-in response

#### Response codes

The authentication flow provides several response codes of which the most common are as follows:
`Activity.RESULT_OK` if a user is signed in, `Activity.RESULT_CANCELED` if the user manually canceled the sign in,
`ErrorCodes.NO_NETWORK` if sign in failed due to a lack of network connectivity,
and `ErrorCodes.UNKNOWN_ERROR` for all other errors.
Typically, the only recourse for most apps if sign in fails is to ask
the user to sign in again later, or proceed with anonymous sign-in if supported.

```java
private void onSignInResult(FirebaseAuthUIAuthenticationResult result) {
    IdpResponse response = result.getIdpResponse();

    if (result.getResultCode() == RESULT_OK) {
        // Successfully signed in
        startActivity(SignedInActivity.createIntent(this, response));
        finish();
    } else {
        // Sign in failed
        if (response == null) {
            // User pressed back button
            showSnackbar(R.string.sign_in_cancelled);
            return;
        }

        if (response.getError().getErrorCode() == ErrorCodes.NO_NETWORK) {
            showSnackbar(R.string.no_internet_connection);
            return;
        }

        showSnackbar(R.string.unknown_error);
        Log.e(TAG, "Sign-in error: ", response.getError());
    }
}
```

Alternatively, you can register a listener for authentication state changes;
see the Firebase Auth documentation to
[get the currently signed-in user](https://firebase.google.com/docs/auth/android/manage-users#get_the_currently_signed-in_user)
and [register an AuthStateListener](https://firebase.google.com/docs/reference/android/com/google/firebase/auth/FirebaseAuth.html#addAuthStateListener(com.google.firebase.auth.FirebaseAuth.AuthStateListener)).

Note: if you choose to use an `AuthStateListener`, make sure to unregister it before launching
the FirebaseUI flow and re-register it after the flow returns. FirebaseUI performs auth operations
internally which may trigger the listener before the flow is complete.

#### ID tokens

To retrieve the ID token that the IDP returned, you can extract an `IdpResponse` from the result
Intent.

```java
private void onSignInResult(FirebaseAuthUIAuthenticationResult result) {
    if (result.getResultCode() == RESULT_OK) {
        // Successfully signed in
       IdpResponse response = result.getIdpResponse();
       startActivity(new Intent(this, WelcomeBackActivity.class)
               .putExtra("my_token", response.getIdpToken()));
    }
}
```

Twitter also returns an AuthToken Secret which can be accessed with `response.getIdpSecret()`.

#### User metadata

While `IdpResponse` provides user information about a specific sign-in instance, it is usually
preferable to find the user name, email, and other metadata directly from the currently signed-in
`FirebaseUser` instance (`auth.getCurrentUser()`). For example, you could determine if the user
who just signed in is an existing or new one by comparing the user's creation and last sign-in time:

```java
FirebaseUserMetadata metadata = auth.getCurrentUser().getMetadata();
if (metadata.getCreationTimestamp() == metadata.getLastSignInTimestamp()) {
    // The user is new, show them a fancy intro screen!
} else {
    // This is an existing user, show them a welcome back screen.
}
```

### Silent sign-in

If a user is not currently signed in, then a silent sign-in process can be started first before
displaying any UI to provide a seamless experience. Silent sign-in uses saved Smart Lock credentials
and returns a successful `Task` only if the user has been fully signed in with Firebase.

Here's an example of how you could use silent sign-in paired with Firebase anonymous sign-in to get
your users up and running as fast as possible:

```java
List<IdpConfig> providers = getSelectedProviders();
AuthUI.getInstance().silentSignIn(this, providers)
        .continueWithTask(this, new Continuation<AuthResult, Task<AuthResult>>() {
    @Override
    public Task<AuthResult> then(@NonNull Task<AuthResult> task) {
        if (task.isSuccessful()) {
            return task;
        } else {
            // Ignore any exceptions since we don't care about credential fetch errors.
            return FirebaseAuth.getInstance().signInAnonymously();
        }
    }
}).addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
    @Override
    public void onComplete(@NonNull Task<AuthResult> task) {
        if (task.isSuccessful()) {
            // Signed in! Start loading data
        } else {
            // Uh oh, show error message
        }
    }
});
```

### Sign out

With the integrations provided by AuthUI, signing out a user is a multi-stage process:

1. The user must be signed out of the FirebaseAuth instance.
1. Smart Lock for Passwords must be instructed to disable automatic sign-in, in
   order to prevent an automatic sign-in loop that prevents the user from
   switching accounts.
1. If the current user signed in using either Google or Facebook, the user must
   also be signed out using the associated API for that authentication method.
   This typically ensures that the user will not be automatically signed-in
   using the current account when using that authentication method again from
   the authentication method picker, which would also prevent the user from
   switching between accounts on the same provider.

In order to make this process easier, AuthUI provides a simple `signOut` method
to encapsulate this behavior. The method returns a `Task` which is marked
completed once all necessary sign-out operations are completed:

```java
public void onClick(View v) {
if (v.getId() == R.id.sign_out) {
    AuthUI.getInstance()
        .signOut(this)
        .addOnCompleteListener(new OnCompleteListener<Void>() {
            public void onComplete(@NonNull Task<Void> task) {
                // user is now signed out
                startActivity(new Intent(MyActivity.this, SignInActivity.class));
                finish();
            }
        });
    }
}
```

### Deleting accounts

With the integrations provided by FirebaseUI Auth, deleting a user is a multi-stage process:

1. The user must be deleted from Firebase Auth.
1. Smart Lock for Passwords must be told to delete any existing Credentials for the user, so
   that they are not automatically prompted to sign in with a saved credential in the future.

This process is encapsulated by the `AuthUI.delete()` method, which returns a `Task` representing
the entire operation:

```java
AuthUI.getInstance()
        .delete(this)
        .addOnCompleteListener(new OnCompleteListener<Void>() {
            @Override
            public void onComplete(@NonNull Task<Void> task) {
                if (task.isSuccessful()) {
                    // Deletion succeeded
                } else {
                    // Deletion failed
                }
            }
        });
```

### Upgrading anonymous users

#### Enabling anonymous user upgrade

When an anonymous user signs in or signs up with a permanent account, you want
to be sure that the user can continue with what they were doing before signing up.
For example, an anonymous user might have items in their shopping cart.
At check-out, you prompt the user to sign in or sign up. After the user is
signed in, the user's shopping cart should contain any items the user added
while signed in anonymously.

To support this behavior, FirebaseUI makes it easy to "upgrade" an anonymous
account to a permanent account. To do so, simply call `enableAnonymousUsersAutoUpgrade()`
when you configure the sign-in UI (this option is disabled by default).

For example:
```java
Intent signInIntent =
    AuthUI.getInstance()
        .createSignInIntentBuilder()
        .enableAnonymousUsersAutoUpgrade()
        ...
        .build();
```

With this enabled, FirebaseUI will link the credential on sign-in with the anonymous account
using Firebase Auth's `linkWithCredential` method:
```java
FirebaseAuth.getInstance().getCurrentUser().linkWithCredential(permanentCredential);
```

#### Handling anonymous user upgrade merge conflicts

There is an issue when an anonymous user tries to upgrade to an existing Firebase user.

For example, a user may have previously signed up with a Google credential on a different device.
If they are signed in anonymously and they attempt to upgrade with the existing Google account,
a `FirebaseAuthUserCollisionException` will be thrown by Firebase Auth as an existing user
cannot be linked to another existing user. No two users can share the same credential. In this case,
we need to merge the data from both users before we can upgrade the anonymous user.

The process of storing the anonymous users data, signing in with the credential, and copying the
data over to the existing account is left to the developer.

When linking is unsuccessful due to user collision, an error with code
`ErrorCodes.ANONYMOUS_UPGRADE_MERGE_CONFLICT` will be returned to the callback of your `ActivityResultLauncher`. A valid
non-anonymous credential can be obtained from the `IdpResponse` via `getCredentialForLinking()`.

**Example:**
```java
private void onSignInResult(FirebaseAuthUIAuthenticationResult result) {
    IdpResponse response = result.getIdpResponse();

    if (result.getResultCode() == RESULT_OK) {
        // Successfully signed in
        // ...
    } else {
        // Sign in failed
        if (response.getError().getErrorCode() == ErrorCodes.ANONYMOUS_UPGRADE_MERGE_CONFLICT) {
            // Store relevant anonymous user data
            ...
            // Get the non-anonymous credential from the response
            AuthCredential nonAnonymousCredential = response.getCredentialForLinking();
            // Sign in with credential 
            FirebaseAuth.getInstance().signInWithCredential(nonAnonymousCredential)
                .addOnSuccessListener(new OnSuccessListener<AuthResult>() {
                    @Override
                    public void onSuccess(AuthResult result) {
                        // Copy over anonymous user data to signed in user
                        ...
                    }
                });
        }
    }
    updateUI();
}
```

### Custom Layout

The first screen shown in most cases is the auth method picker screen, where the user selects
from a list of authentication methods. While customization in other screens of FirebaseUI is
limited to themes, this screen can be fully customized with your own XML layout.

To customize the auth method picker screen, build an `AuthMethodPickerLayout` object and pass
it to the `SignInIntentBuilder` before launching the AuthUI flow:

```java
// You must provide a custom layout XML resource and configure at least one
// provider button ID. It's important that that you set the button ID for every provider
// that you have enabled. 
AuthMethodPickerLayout customLayout = new AuthMethodPickerLayout
    .Builder(R.layout.your_custom_layout_xml)
    .setGoogleButtonId(R.id.bar)
    .setEmailButtonId(R.id.foo)
    // ...
    .setTosAndPrivacyPolicyId(R.id.baz)
    .build();
    
Intent signInIntent =
    AuthUI.getInstance(this).createSignInIntentBuilder()
        // ...
        .setAuthMethodPickerLayout(customLayout)
        .build();
```

### Strings

Ensure an `app_name` resource is defined your `strings.xml` file like so:

```xml
<resources>
    <string name="app_name">My App</string>
    <!-- ... -->
</resources>
```

If you wish to change other strings in the UI, the existing strings can be overridden
by name in your application. See the module's [strings.xml](src/main/res/values/strings.xml) file
and simply redefine a string to change it:

```xml
<resources>
    <!-- was "Signing up..." -->
    <string name="fui_progress_dialog_signing_up">Creating your shiny new account...</string>
</resources>
```

**Note:** String resource names aren't considered part of the public API and might
therefore change and break your app between library updates. We recommend looking
at a diff of the `strings.xml` file before updating FirebaseUI.

## OAuth scope customization

### Google
By default, FirebaseUI requests the `email` and `profile` scopes when using Google Sign-In. If you
would like to request additional scopes from the user, call `setScopes` on the
`AuthUI.IdpConfig.GoogleBuilder` when initializing FirebaseUI.

```java
// For a list of all scopes, see:
// https://developers.google.com/identity/protocols/googlescopes
AuthUI.IdpConfig googleIdp = new AuthUI.IdpConfig.GoogleBuilder()
        .setScopes(Arrays.asList(Scopes.GAMES))
        .build();

Intent signInIntent =
        AuthUI.getInstance()
                .createSignInIntentBuilder()
                .setAvailableProviders(Arrays.asList(googleIdp, ...))
                .build();
```

### Facebook

By default, FirebaseUI requests the `email` and `public_profile` permissions when initiating
Facebook Login. If you would like to request additional permissions from the user, call
`setPermissions` on the `AuthUI.IdpConfig.FacebookBuilder` when initializing FirebaseUI.

```java
// For a list of permissions see:
// https://developers.facebook.com/docs/facebook-login/permissions

AuthUI.IdpConfig facebookIdp = new AuthUI.IdpConfig.FacebookBuilder()
        .setPermissions(Arrays.asList("user_friends"))
        .build();

Intent signInIntent =
        AuthUI.getInstance()
                .createSignInIntentBuilder()
                .setAvailableProviders(Arrays.asList(facebookIdp, ...))
                .build();
```

### Twitter

Twitter permissions can only be configured through [Twitter's developer console](https://apps.twitter.com/).