OAuth-based App Flip Linking (App Flip) allows your users to quickly
link their accounts in your authentication system to their Google Accounts.
If your app is installed on your user's phone when they initiate the account
linking process, they are seamlessly flipped to your app to obtain user
authorization.

This approach provides a faster linking process since the user does
not have to re-enter their username and password to authenticate; instead,
App Flip leverages the credentials from the user's account on your app. Once a
user has linked their Google Account with your app, they can take advantage of
any integrations that you have developed.

You can set up App Flip for both iOS and Android apps.
![This figure shows the steps for a user to link their Google account
to your authentication system. The first screenshot shows how a user
can select your app if their Google account is linked to your app.
The second screenshot shows the confirmation for linking their
Google account with your app. The third screenshot shows a
successfully linked user account in the Google app.](https://developers.google.com/static/identity/images/app-flip-flow.png) **Figure 1.** Account linking on a user's phone with App Flip.

## Requirements

To implement App Flip, you must fulfill the following requirements:

- You must have an Android or iOS app.
- You must own, manage and maintain an OAuth 2.0 server which supports the OAuth 2.0 authorization code flow.

> [!NOTE]
> **Note:** Confirm that your OAuth2 implementation or provider supports the authorization code flow along with App Flip redirect URLs and client_ids as described in our guides.

### OAuth-based App Flip Flow

The following sequence diagram details the interaction between the User,
Google App, Your App, and Your Authorization Server for App Flip.
User Google App Your App Google Server Your Auth Server 1. Initiates linking 2. Deep link to Your App 3. Show Consent Screen 4. User Grants Consent 5. Get Auth Code 6. authorization_code 7. Return to Google App 8. Pass code to Google Server 9. Token Exchange (POST) 10. access_token, refresh_token 11. Store user tokens 12. Access user resources **Figure 2.** The sequence of events in the App Flip flow. If an authorization code is provided, the token exchange happens server-to-server, the same way it does in the browser-based OAuth linking flow.

### Roles and responsibilities

The following table defines the roles and responsibilities of the actors in the
App Flip flow.

| Actor / Component | GAL Role | Responsibilities |
|---|---|---|
| **Google App / Server** | OAuth Client | Initiates the linking process, triggers a deep link to your mobile app, exchanges the authorization code for tokens, and securely stores them to access your service's APIs. |
| **Your App** | Authorization Agent | Authenticates the user (typically using existing app credentials), obtains consent, and retrieves an authorization code from your server. |
| **Your Authorization Server** | Authorization Server | Validates authorization codes and refresh tokens, and issues access tokens to the Google Server. |

For more information on the OAuth linking authorization code flow, see
[Implement your OAuth server](https://developers.google.com/assistant/identity/oauth2?oauth=code#implement_your_oauth_server).

> [!CAUTION]
> **Caution:** For OAuth-based App Flip, you can implement either the [OAuth-based Google Sign-in "Streamlined" linking type](https://developers.google.com/assistant/identity/gsi-oauth-concept-guide) or the [OAuth linking type](https://developers.google.com/assistant/identity/oauth-concept-guide). Both of these linking types must use the *authorization code flow* for App Flip to work.

## Design guidelines

This section describes the design requirements and recommendations for the App
Flip account linking consent screen. After Google calls your app, your app
displays the consent screen to the user.

### Requirements

1. You must communicate that the user's account is being linked to Google, **not** to a specific Google product, such as Google Home or Google Assistant.

### Recommendations

We recommend that you do the following:

1. **Display Google's Privacy Policy.** Include a link to
   [Google's Privacy Policy](http://policies.google.com)
   on the consent screen.

2. **Data to be shared.** Use clear and concise language to tell the user what
   data of theirs Google requires and why.

3. **Clear call-to-action.** State a clear call-to-action on your consent
   screen, such as "Agree and link." This is because users need to
   understand what data they're required to share with Google to link their
   accounts.

4. **Ability to deny or cancel.** Provide a way for users to go back, deny, or
   cancel, if they choose not to link.

5. **Ability to unlink.** Offer a mechanism for users to unlink, such as a
   URL to their account settings on your platform. Alternatively, you can
   include a link to [Google Account](https://myaccount.google.com) where users
   can manage their linked account.

6. **Ability to change user account.** Suggest a method for users to switch
   their account(s). This is especially beneficial if users tend to have
   multiple accounts.

   - If a user must close the consent screen to switch accounts, send a recoverable error to Google so the user can sign in to the desired account with *OAuth linking* and the *implicit* flow.
7. **Include your logo.** Display your company logo on the consent screen.
   Use your style guidelines to place your logo. If you wish
   to also display Google's logo, see
   [Logos and trademarks](https://www.google.com/permissions/logos-trademarks/).

![This figure shows an example consent screen with call-outs to the
individual requirements and recommendations to be followed when
you design a user consent screen.](https://developers.google.com/static/identity/images/app-flip-guidance.png) **Figure 2.** Account linking consent screen design guidelines.

## Set up for OAuth-based App Flip

The following sections describe the prerequisites for OAuth-based App Flip and how to configure your
App Flip project in the Actions console.

### Create
an Action
and set up an OAuth 2.0 server

Before you can configure App Flip, you need to do the following:

- **Create an Action.** To create an Action, follow the instructions in the [Create a project](https://developers.google.com/assistant/conversational/build/projects?tool=builder#create_a_project) section.
- **Set up an OAuth 2.0 server.** For more information about setting up an OAuth server, see [Implement OAuth account linking](https://developers.google.com/assistant/identity/oauth2?oauth=code#implement_oauth_account_linking).

### Configure App Flip in the Actions console

The following section describes how to configure App Flip in the
[Actions console](https://console.actions.google.com/).

> [!NOTE]
> **Note:** Choose which type of platform you want to target. The content of this page reloads to adapt to your choice.

<button value="android" default="">Android</button> <button value="iOS">iOS</button>

1. Click **Develop** in the top navigation. Then, click **Account linking** in the left navigation.
2. Toggle on the switch next to **Account linking.**
3. Under **Account creation** , select **No, I only want to
   allow account creation on my website**.
4. Click **Next**.
5. Under **Linking type** , select **OAuth** and **Authorization code** from the drop-down menus.
6. Click **Next**.
7. Fill out all the fields under **OAuth Client information**. (If App Flip isn't supported, regular OAuth is used as a fallback.)
8. Click **Next**.
9. Under **Use your app for account linking (optional)** , check **Enable for iOS**.
10. Fill out the **Universal Link** field. For more information about universal links, see [Allowing Apps and Websites to Link to your Content](https://developer.apple.com/documentation/uikit/inter-process_communication/allowing_apps_and_websites_to_link_to_your_content).
11. If you want to optionally configure your client, add scopes and click **Add scope** under **Configure your client (optional).** If not, click **Next.**
12. Under Testing instructions, type `test` (or any other string) as a placeholder. (Filling in this field with a test account is only necessary if you are actually submitting your Action to be published.)
13. Click **Save**.


You can now continue to the next section to implement App Flip in your iOS or Android app.

## Implement App Flip in your native apps

To implement App Flip, you need to modify the user authorization code in your
app to accept a deep link from Google.

## Test App Flip on your device

Now that you've created an Action and configured App Flip on the console and in
your app, you can test App Flip on your mobile device. You can use the
Google Assistant app

to test App Flip.

To test App Flip from the Assistant app, follow these steps:

1. Go to the [Actions console](https://console.actions.google.com/) and select your project.
2. Click **Test** in the top navigation.
3. Trigger the account linking flow from the Assistant app:
   1. Open the [Google Assistant app](https://play.google.com/store/apps/details?id=com.google.android.apps.googleassistant).
   2. Click **Settings**.
   3. On the Assistant tab, click **Home Control.**
   4. Click **Add(+)**.
   5. Select your Action from the list of providers. It will be prefixed with "\[test\]" in the list. When you select your \[test\] Action from the list, it should open your app.
   6. Verify that your app was launched and begin testing your authorization flow.