Accounts are linked using industry standard OAuth 2.0 implicit and authorization code flows. Your service must support OAuth 2.0 compliant authorization and token exchange endpoints.
In the implicit flow, Google opens your authorization endpoint in the user's browser. After successful sign in, you return a long-lived access token to Google. This access token is now included in every request sent from Google.
In the authorization code flow, you need two endpoints:
The authorization endpoint, which presents the sign-in UI to your users that aren't already signed in. The authorization endpoint also creates a short-lived authorization code to record users' consent to the requested access.
The token exchange endpoint, which is responsible for two types of exchanges:
- Exchanges an authorization code for a long-lived refresh token and a short-lived access token. This exchange happens when the user goes through the account linking flow.
- Exchanges a long-lived refresh token for a short-lived access token. This exchange happens when Google needs a new access token because the one it had expired.
Choose an OAuth 2.0 flow
Although the implicit flow is simpler to implement, Google recommends that access tokens issued by the implicit flow never expire. This is because the user is forced to link their account again after a token expires with the implicit flow. If you need token expiration for security reasons, we strongly recommend that you use the authorization code flow instead.
This section describes the design requirements and recommendations for the user screen that you host for OAuth linking flows. After it's called by Google's app, your platform displays a sign in to Google page and account linking consent screen to the user. The user is directed back to Google's app after giving their consent to link accounts.
- You must communicate that the user’s account will be linked to Google, not a specific Google product like Google Home or Google Assistant.
We recommend that you do the following:
Data to be shared. Use clear and concise language to tell the user what data of theirs Google requires and why.
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.
Ability to cancel. Provide a way for users to go back or cancel, if they choose not to link.
Clear sign-in process. Ensure that users have clear method for signing in to their Google account, such as fields for their username and password or Sign in with Google.
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.
Create the project
To create your project to use account linking:
- Go to the Google API Console.
- Click Create project.
- Enter a name or accept the generated suggestion.
- Confirm or edit any remaining fields.
- Click Create.
To view your project ID:
- Go to the Google API Console.
- Find your project in the table on the landing page. The project ID appears in the ID column.
Configure your OAuth Consent Screen
The Google Account Linking process includes a consent screen which tells users the application requesting access to their data, what kind of data they are asking for and the terms that apply. You will need to configure your OAuth consent screen before generating a Google API client ID.
- Open the OAuth consent screen page of the Google APIs console.
- If prompted, select the project you just created.
On the "OAuth consent screen" page, fill out the form and click the “Save” button.
Application name: The name of the application asking for consent. The name should accurately reflect your application and be consistent with the application name users see elsewhere. The application name will be shown on the Account Linking consent screen.
Application logo: An image on the consent screen that will help users recognize your app. The logo is shown on Account linking consent screen and on account settings
Support email: For users to contact you with questions about their consent.
Scopes for Google APIs: Scopes allow your application to access your user's private Google data. For the Google Account Linking use case, default scope (email, profile, openid) is sufficient, you don’t need to add any sensitive scopes. It is generally a best practice to request scopes incrementally, at the time access is required, rather than up front. Learn more.
Authorized domains: To protect you and your users, Google only allows applications that authenticate using OAuth to use Authorized Domains. Your applications' links must be hosted on Authorized Domains. Learn more.
Application Homepage link: Home page for your application. Must be hosted on an Authorized Domain.
Application Terms of Service link (Optional): Must be hosted on an Authorized Domain.
Figure 1. Google Account Linking Consent Screen for a fictitious Application, Tunery
Check "Verification Status", if your application needs verification then click the "Submit For Verification" button to submit your application for verification. Refer to OAuth verification requirements for details.
Implement your OAuth server
To support the OAuth 2.0 implicit flow, your service makes an authorization endpoint available by HTTPS. This endpoint is responsible for authentication and obtaining consent from users for data access. The authorization endpoint presents a sign-in UI to your users that aren't already signed in and records consent to the requested access.
When a Google application needs to call one of your service's authorized APIs, Google uses this endpoint to get permission from your users to call these APIs on their behalf.
A typical OAuth 2.0 implicit flow session initiated by Google has the following flow:
- Google opens your authorization endpoint in the user's browser. The user signs in, if not signed in already, and grants Google permission to access their data with your API, if they haven't already granted permission.
- Your service creates an access token and returns it to Google. To do so, redirect the user's browser back to Google with the access token attached to the request.
- Google calls your service's APIs and attaches the access token with each request. Your service verifies that the access token grants Google authorization to access the API and then completes the API call.
Handle authorization requests
When a Google application needs to perform account linking via an OAuth 2.0 implicit flow, Google sends the user to your authorization endpoint with a request that includes the following parameters:
|Authorization endpoint parameters|
||The client ID you assigned to Google.|
||The URL to which you send the response to this request.|
||A bookkeeping value that is passed back to Google unchanged in the redirect URI.|
||The type of value to return in the response. For the OAuth 2.0 implicit
flow, the response type is always
||The Google Account language setting in RFC5646 format used to localize your content in the user's preferred language.|
For example, if your authorization endpoint is available at
https://myservice.example.com/auth, a request might look like the following:
For your authorization endpoint to handle sign-in requests, do the following steps:
redirect_urivalues to prevent granting access to unintended or misconfigured client apps:
- Confirm that the
client_idmatches the client ID you assigned to Google.
- Confirm that the URL specified by the
redirect_uriparameter has the following form:
- Confirm that the
Check if the user is signed in to your service. If the user isn't signed in, complete your service's sign-in or sign-up flow.
Generate an access token for Google to use to access your API. The access token can be any string value, but it must uniquely represent the user and the client the token is for and must not be guessable.
Send an HTTP response that redirects the user's browser to the URL specified by the
redirect_uriparameter. Include all of the following parameters in the URL fragment:
access_token: The access token you just generated
token_type: The string
state: The unmodified state value from the original request
The following is an example of the resulting URL:
Google's OAuth 2.0 redirect handler receives the access token and confirms
state value hasn't changed. After Google has obtained an
access token for your service, Google attaches the token to subsequent calls
to your service APIs.
Validating your implementation
You can validate your implementation by using the OAuth 2.0 Playground tool.
In the tool, do the following steps:
- Click Configuration to open the OAuth 2.0 Configuration window.
- In the OAuth flow field, select Client-side.
- In the OAuth Endpoints field, select Custom.
- Specify your OAuth 2.0 endpoint and the client ID you assigned to Google in the corresponding fields.
- In the Step 1 section, don't select any Google scopes. Instead, leave this field blank or type a scope valid for your server (or an arbitrary string if you don't use OAuth scopes). When you're done, click Authorize APIs.
- In the Step 2 and Step 3 sections, go through the OAuth 2.0 flow and verify that each step works as intended.
You can validate your implementation by using the Google Account Linking Demo tool.
In the tool, do the following steps:
- Click the Sign-in with Google button.
- Choose the account you'd like to link.
- Enter the service ID.
- Optionally enter one or more scopes that you will request access for.
- Click Start Demo.
- When prompted, confirm that you may consent and deny the linking request.
- Confirm that you are redirected to your platform.