使用 OAuth 連結 Google 帳戶

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帳戶連結會使用業界標準的 OAuth 2.0 隱含和授權碼流程。您的服務必須支援符合 OAuth 2.0 標準的授權和權杖交換端點。

在隱含流程中，Google 會在使用者的瀏覽器中開啟授權端點。成功登入後，會將長期存取權杖傳回 Google。這個存取權杖現在已納入 Google 發出的每項要求。

在授權碼流程中，您需要兩個端點：

• 授權端點，會為尚未登入的使用者顯示登入 UI。授權端點也會建立短效授權碼，記錄使用者對所要求存取權的同意聲明。

• 權杖交換端點，負責兩種交換：

  1. 交換授權碼用於長期更新權杖和短期存取權杖。使用者進行帳戶連結流程時，就會發生這個交換。
  2. 這個外掛程式能使用長期更新權杖做為短期存取權杖。 如果 Google 需要新的存取權存證，因為舊的存證已過期，就會發生此交換。

選擇 OAuth 2.0 流程

雖然隱含流程的實作方式較簡單，但 Google 建議隱含流程發出的存取權杖永遠不會過期。這是因為權杖過期後，系統必須要求使用者再次連結帳戶。如果您基於安全性考量而需要代碼到期，強烈建議您改用授權程式碼流程。

設計指南

本節說明針對 OAuth 連結流程所託管使用者畫面的設計需求和建議。Google 的應用程式呼叫後，您的平台會向使用者顯示登入 Google 頁面和帳戶連結同意畫面。使用者同意連結帳戶後，系統會將他們導向 Google 的應用程式。

需求條件

1. 您必須說明使用者的帳戶將連結至 Google，而不是 Google Home 或 Google 助理等特定 Google 產品。

建議

建議您採取以下做法：

1. 顯示《Google 隱私權政策》。在同意畫面加入 Google 隱私權政策連結。

2. 要共用的資料。使用簡潔明瞭的表達方式，向使用者說明 Google 需要他們的哪些資料，以及原因。

3. 明確的行動號召。在同意聲明畫面上明確列出行動號召，例如「同意並連結」。這是因為使用者需要瞭解自己必須與 Google 分享哪些資料，才能連結帳戶。

4. 可取消訂閱。如果使用者選擇不連結，請提供返回或取消的選項。

5. 清除登入程序。請確認使用者有明確的方法登入 Google 帳戶，例如使用者名稱和密碼欄位，或使用 Google 帳戶登入。

6. 可取消連結。提供使用者解除連結的機制，例如平台上帳戶設定的網址。或者，您也可以加入 Google 帳戶的連結，讓使用者能管理已連結帳戶。

7. 變更使用者帳戶的功能。建議使用者切換帳戶的方法。如果使用者傾向擁有多個帳戶，這項功能就特別實用。

   • 如果使用者必須關閉同意畫面才能切換帳戶，請將可復原的錯誤傳送給 Google，方便使用者透過 OAuth 連結和隱含流程登入所需帳戶。

8. 加入標誌。在同意畫面上顯示公司標誌。 請依照您的樣式規範放置標誌。如果您也想顯示 Google 的標誌，請參閱標誌和商標。

Create the project

To create your project to use account linking:

1. Go to the Google API Console.
2. Click Create project.
3. Enter a name or accept the generated suggestion.
4. Confirm or edit any remaining fields.
5. Click Create.

要查看您的項目ID：

1. Go to the Google API Console.
2. 在登錄頁面的表格中找到您的項目。項目ID出現在ID列中。

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.

1. Open the OAuth consent screen page of the Google APIs console.
2. If prompted, select the project you just created.

3. 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 Privacy Policy link: Shown on Google Account Linking consent screen. 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

4. 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.

實作 OAuth 伺服器

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:

1. 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.
2. 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.
3. 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:

For example, if your authorization endpoint is available at https://myservice.example.com/auth, a request might look like the following:

GET https://myservice.example.com/auth?client_id=GOOGLE_CLIENT_ID&redirect_uri=REDIRECT_URI&state=STATE_STRING&response_type=token&user_locale=LOCALE

For your authorization endpoint to handle sign-in requests, do the following steps:

1. Verify the client_id and redirect_uri values to prevent granting access to unintended or misconfigured client apps:

   • Confirm that the client_id matches the client ID you assigned to Google.
   • Confirm that the URL specified by the redirect_uri parameter has the following form:

     https://oauth-redirect.googleusercontent.com/r/YOUR_PROJECT_ID
     https://oauth-redirect-sandbox.googleusercontent.com/r/YOUR_PROJECT_ID
     

2. 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.

3. 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.

4. Send an HTTP response that redirects the user's browser to the URL specified by the redirect_uri parameter. Include all of the following parameters in the URL fragment:

   • access_token: The access token you just generated
   • token_type: The string bearer
   • state: The unmodified state value from the original request

   The following is an example of the resulting URL:

   https://oauth-redirect.googleusercontent.com/r/YOUR_PROJECT_ID#access_token=ACCESS_TOKEN&token_type=bearer&state=STATE_STRING

Google's OAuth 2.0 redirect handler receives the access token and confirms that the 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.

Handle userinfo requests

The userinfo endpoint is an OAuth 2.0 protected resource that return claims about the linked user. Implementing and hosting the userinfo endpoint is optional, except for the following use cases:

• Linked Account Sign-In with Google One Tap.
• Frictionless subscription on AndroidTV.

After the access token has been successfully retrieved from your token endpoint, Google sends a request to your userinfo endpoint to retrieve basic profile information about the linked user.

For example, if your userinfo endpoint is available at https://myservice.example.com/userinfo, a request might look like the following:

GET /userinfo HTTP/1.1
Host: myservice.example.com
Authorization: Bearer ACCESS_TOKEN

For your userinfo endpoint to handle requests, do the following steps:

1. Extract access token from the Authorization header and return information for the user associated with the access token.
2. If the access token is invalid, return an HTTP 401 Unauthorized error with using the WWW-Authenticate Response Header. Below is an example of a userinfo error response:

   HTTP/1.1 401 Unauthorized
   WWW-Authenticate: error="invalid_token",
   error_description="The Access Token expired"
   

   If a 401 Unauthorized, or any other unsuccessful error response is returned during the linking process, the error will be non-recoverable, the retrieved token will be discarded and the user will have to initiate the linking process again.

3. If the access token is valid, return and HTTP 200 response with the following JSON object in the body of the HTTPS response:

   {
   "sub": "USER_UUID",
   "email": "EMAIL_ADDRESS",
   "given_name": "FIRST_NAME",
   "family_name": "LAST_NAME",
   "name": "FULL_NAME",
   "picture": "PROFILE_PICTURE",
   }

   If your userinfo endpoint returns an HTTP 200 success response, the retrieved token and claims are registered against the user's Google account.

   userinfo endpoint response
   sub	A unique ID that identifies the user in your system.
   email	Email address of the user.
   given_name	Optional: First name of the user.
   family_name	Optional: Last name of the user.
   name	Optional: Full name of the user.
   picture	Optional: Profile picture of the user.

驗證實作

You can validate your implementation by using the OAuth 2.0 Playground tool.

In the tool, do the following steps:

1. Click Configuration settings to open the OAuth 2.0 Configuration window.
2. In the OAuth flow field, select Client-side.
3. In the OAuth Endpoints field, select Custom.
4. Specify your OAuth 2.0 endpoint and the client ID you assigned to Google in the corresponding fields.
5. 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.
6. 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:

1. Click the Sign-in with Google button.
2. Choose the account you'd like to link.
3. Enter the service ID.
4. Optionally enter one or more scopes that you will request access for.
5. Click Start Demo.
6. When prompted, confirm that you may consent and deny the linking request.
7. Confirm that you are redirected to your platform.