Google is transitioning third-party smart home account linking to be handled fully and independently within the Google Home app. Updates to your integration may be needed before October 30, 2026. For more information, see the Account linking migration guide.

App Flip for iOS

Once you have an OAuth 2.0 implementation, you can optionally configure OAuth-based App Flip, which allows your iOS users to more quickly link their accounts in your authentication system to their Google Accounts. The following sections describe how to design and implement App Flip for your Cloud-to-cloud integration on iOS.

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

You must have a Google authorization statement such as "Once linked, Google will have permission to control your devices."
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.
You must state a clear call-to-action on your consent screen and use the wording "Agree and link" for linking action. This is because users need to understand what data they're required to share with Google to link their accounts.
You must provide a way for users to go back, deny or cancel, if they choose not to link. Use the wording "Cancel" for the cancel action.
You must implement this workflow: After clicking "Agree and link", you must show linking success and redirect the user back to the Google Home app automatically. The user should now see the linked device on the Google Home app with your action. After clicking "Cancel" you should redirect the user back to the Google Home app.

Recommendations

We recommend that you do the following:

Display Google's Privacy Policy. Include a link to Google's Privacy Policy on the consent screen.
Data to be shared. Use clear and concise language to tell the user what data of theirs Google requires and why.
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 where users can manage their linked account.
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.
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.

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. — Figure 1: 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 Google Home Developer Console.

Create a Cloud-to-cloud integration and set up an OAuth 2.0 server

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

Set up an OAuth 2.0 server. For more information about setting up an OAuth server, see Implement an OAuth 2.0 server.
Create a Cloud-to-cloud integration. To create an integration, follow the instructions in Create a Cloud-to-cloud integration.

Configure App Flip in the Developer Console

The following section describes how to configure App Flip in the Developer Console.

Fill out all the fields under OAuth Client information. (If App Flip isn't supported, regular OAuth is used as a fallback.)
Under Use your app for account linking(optional), check Enable for iOS.
Fill out the Universal Link field. For more information about universal links, see Allowing Apps and Websites to Link to your Content.
If you want to optionally configure your client, add scopes and click Add scope under Configure your client (optional).
Click Save.

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

OAuth-based App Flip linking (App Flip) opens your iOS app from a Google app to help the Google app user link their account more easily. You need to make minor code changes to your iOS app to implement this feature.

In this document, you learn how to modify your iOS app to support App Flip.

Try the sample

The App Flip sample app demonstrates an account linking integration on iOS that's App Flip-compatible. You can use this app to verify how to respond to an incoming App Flip universal link from Google mobile apps.

The sample app is preconfigured to integrate with the App Flip Test Tool for iOS, which you can use to verify your iOS app's integration with App Flip before you configure account linking with Google. This app simulates the universal link triggered by Google mobile apps when App Flip is enabled.

How it works

The following are the flow steps that the Google app and your app take when App Flip occurs:

The Google app attempts to open your app’s universal link. It's able to open your app if it's installed on the user’s device and associated with the universal link. See Supporting Universal Links for details.
Your app checks that the client_id and redirect_uri parameter encoded in the incoming URL matches the expected Google universal link.
Your app requests an authorization code from your OAuth2 server. At the end of this flow, your app returns either an authorization code or an error to the Google app. To do this, it opens Google's universal link with appended parameters for the authorization code or error.
The Google app handles the incoming Google universal link and continues with the rest of the flow. If an authorization code is provided, the linking is completed immediately. The token exchange happens server-to-server, the same way it does in the browser-based OAuth linking flow. If an error code is returned, the linking flow continues with the alternative options.

Modify your iOS app to support App Flip

To support App Flip, make the following code changes to your iOS app:

Handle NSUserActivityTypeBrowsingWeb in your App Delegate.
Capture redirect_uri and state parameters from the URL to use later.

Check that redirect_uri matches this format:

https://oauth-redirect.googleusercontent.com/a/GOOGLE_APP_BUNDLE_ID
https://oauth-redirect-sandbox.googleusercontent.com/a/GOOGLE_APP_BUNDLE_ID

Verify that the client ID matches the expected value. Use the following code sample:

func application(_ application: UIApplication,
                 continue userActivity: NSUserActivity,
                 restorationHandler: @escaping ([Any]?) -> Void) -> Bool
{
    guard userActivity.activityType == NSUserActivityTypeBrowsingWeb,
        let incomingURL = userActivity.webpageURL,
        let components = URLComponents(url: incomingURL, resolvingAgainstBaseURL: false),
        let params = components.queryItems else {
            return false
    }

    if let clientId = params.filter({$0.name == "client_id"}).first?.value,
        let state = params.filter({$0.name == "state"}).first?.value,
        let redirectUri = params.filter({$0.name == "redirect_uri"}).first?.value {

        // Save the redirect_uri and state for later...

        // Verify the client id
        return (clientId == GOOGLE_CLIENT_ID)
    } else {
        // Missing required parameters
        return false
    }
}

Upon successful authorization, call the redirect URI with the authorization code. Use the following code sample:

func returnAuthCode(code: String, state: String, redirectUri: String) {
    var redirectURL = URL(string: redirectUri)
    var components = URLComponents(url: redirectURL, resolvingAgainstBaseURL: false)

    // Return the authorization code and original state
    let paramAuthCode = URLQueryItem(name: "code", value: code)
    let paramState = URLQueryItem(name: "state", value: state)
    components?.queryItems = [paramAuthCode, paramState]
    if let resultURL = components?.url {
        UIApplication.shared.open(
            resultURL,
            options: [UIApplicationOpenURLOptionUniversalLinksOnly : true],
            completionHandler: nil)
    }
}

If an error occurred, attach an error result to the redirect URI instead. Use the following code sample:

func returnError(redirectUri: String) {
    var redirectURL = URL(string: redirectUri)
    var components = URLComponents(url: redirectURL, resolvingAgainstBaseURL: false)

    // Return the authorization code and original state
    let paramError = URLQueryItem(name: "error", value: "invalid_request")
    let paramDescription = URLQueryItem(name: "error_description", value: "Invalid Request")
    components?.queryItems = [paramError, paramDescription]
    if let resultURL = components?.url {
        UIApplication.shared.open(
            resultURL,
            options: [UIApplicationOpenURLOptionUniversalLinksOnly : true],
            completionHandler: nil)
    }
}

Query parameters for your app’s universal link

When opened by the Google app, your app’s universal link includes the following query parameters:

client_id (String): Google client_id that's registered under your app.
scope (List of String): A list of space-separated scopes requested.
state (String): A nonce used by Google to verify that the authorization result is in response to Google’s outgoing request.
redirect_uri (String): Google's universal link. The "flip" URI to open the Google app and pass results.

Query parameters for Google’s universal link

Parameters used when the authorization result is returned successfully:

code (String): The value of the authorization code, if available.
state (String): The exact value received from the incoming universal link.

Parameters used when the authorization result is returned unsuccessfully:

error (String), with the following values:
- cancelled: A recoverable error. The Google app will attempt account linking using the authorization URL. Some examples are the user failing to sign in, a device being offline or a connection timing out.
- unrecoverable: An unrecoverable error. For example, the user attempts to link with a disabled account.The Google app will abort account linking.
- invalid_request: The request parameters are invalid or missing. This is a recoverable error. The Google app will attempt account linking using the authorization URL.
- access_denied: The user rejects the consent request. This is a non-recoverable error; the Google app aborts linking.
error_description (String, optional): A user-friendly error message.

Note: For more information on possible errors and the optional contents of the error_description field, see the OAuth 2.0 standard.

For all error types, you must return the response data to the specified REDIRECT_URI to ensure the appropriate fallback is triggered.

Modify your authorization endpoint to support App Flip

Configure your platform to accept requests using Google's App Flip redirect URLs:

Google Home app

https://oauth-redirect.googleusercontent.com/a/com.google.Chromecast.dev
https://oauth-redirect.googleusercontent.com/a/com.google.Chromecast.enterprise
https://oauth-redirect.googleusercontent.com/a/com.google.Chromecast
https://oauth-redirect-sandbox.googleusercontent.com/a/com.google.Chromecast.dev
https://oauth-redirect-sandbox.googleusercontent.com/a/com.google.Chromecast.enterprise
https://oauth-redirect-sandbox.googleusercontent.com/a/com.google.Chromecast

Google Assistant app

https://oauth-redirect.googleusercontent.com/a/com.google.OPA.dev
https://oauth-redirect.googleusercontent.com/a/com.google.OPA.enterprise
https://oauth-redirect.googleusercontent.com/a/com.google.OPA
https://oauth-redirect-sandbox.googleusercontent.com/a/com.google.OPA.dev
https://oauth-redirect-sandbox.googleusercontent.com/a/com.google.OPA.enterprise
https://oauth-redirect-sandbox.googleusercontent.com/a/com.google.OPA

For the Google Home app (GHA), Smart Home account linking uses the com.google.Chromecast redirect URLs. Ensure your authorization server allows these redirect URLs.

Check that client_id and the URL specified by the redirect_uri parameter match the expected values when a request is received. If the client verification fails, return the error invalid_request to the redirect_uri.

Test App Flip on your device

Now that you've created a Cloud-to-cloud integration 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 Home app to test App Flip.

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

Go to the Developer Console and select your project.
Go to Cloud-to-cloud > Test.
Trigger the account linking flow from the Home app:

Open the Google Home app (GHA).
Click the + button.
Click Set up device.
Click Have something already set up?
Select your Cloud-to-cloud integration from the list of providers. It will be prefixed with “[test]” in the list. When you select your [test] integration from the list, it should open your app.
Verify that your app was launched and begin testing your authorization flow.

Android

Identify and sync