導入 OAuth 2.0 伺服器

每個Cloud-to-cloud整合都必須包含使用者驗證機制。

驗證可讓您將使用者的 Google 帳戶連結至驗證系統中的使用者帳戶。這樣一來，當智慧住宅服務收到意圖時，您就能識別使用者。Google 智慧住宅僅支援使用授權碼流程的 OAuth。

本頁說明如何設定 OAuth 2.0 伺服器，使其與 Cloud-to-cloud 整合服務搭配運作。

透過 OAuth 連結 Google 帳戶

在授權碼流程中，您需要兩個端點：

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

• 權杖交換端點，負責處理兩種類型的交換作業：

  1. 將授權碼換成長期更新權杖和短期存取權杖。使用者完成帳戶連結流程時，就會發生這項交換作業。
  2. 將長期更新權杖換成短期存取權杖。 如果 Google 的存取權杖已過期，就需要新的權杖，此時就會進行這項交換程序。

設計指南

本節說明您為 OAuth 連結流程代管的使用者畫面設計規定和建議。Google 應用程式呼叫後，平台會向使用者顯示 Google 登入頁面和帳戶連結同意畫面。使用者同意連結帳戶後，系統會將他們帶回 Google 應用程式。

需求條件

1. 您必須告知使用者，他們的帳戶將連結至 Google，而非 Google Home 或 Google 助理等特定 Google 產品。
2. 您必須提供 Google 授權聲明，例如「登入即表示授權 Google 控制您的裝置」。請參閱 Google Home 開發人員政策的「Google 裝置控制授權」一節。
3. 您必須開啟網頁 OAuth 連結頁面，並確保使用者有清楚的 Google 帳戶登入方式，例如使用者名稱和密碼欄位。請勿使用 Google 登入 (GSI) 方法，讓使用者不必前往網頁 OAuth 連結頁面即可連結帳戶。此舉違反了 Google 政策。
4. 您必須在 OAuth 連結頁面中加入至少一個下列項目，指出使用者要連結的整合服務：
   • 公司標誌
   • 公司名稱
   • 整合作業名稱
   • 應用程式圖示

建議

建議您採取下列做法：

1. 顯示 Google 隱私權政策。在同意畫面中加入 Google 隱私權政策的連結。

2. 要分享的資料。請使用簡潔明瞭的用語，告知使用者 Google 需要哪些資料，以及原因。

3. 明確的行動號召。在同意聲明畫面中提供明確的行動號召，例如「同意並連結」。這是因為使用者必須瞭解連結帳戶時，需要與 Google 分享哪些資料。

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方式。

5. 清楚的登入程序。確保使用者有明確的 Google 帳戶登入方式，例如使用者名稱和密碼欄位，或是「使用 Google 帳戶登入」。

6. 可取消連結。提供使用者取消連結的機制，例如平台帳戶設定的網址。或者，您也可以加入Google 帳戶的連結，讓使用者管理已連結的帳戶。

7. 可變更使用者帳戶。建議使用者切換帳戶的方法。如果使用者通常有多個帳戶，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，讓使用者透過 OAuth 連結登入所需帳戶。

8. 加入您的標誌。在同意畫面上顯示公司標誌。 請按照樣式指南放置標誌。如要顯示 Google 標誌，請參閱「標誌和商標」。

授權碼流程

An OAuth 2.0 server implementation of the authorization code flow consists of two endpoints, which your service makes available by HTTPS. The first endpoint is the authorization endpoint, which is responsible for finding or 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. The second endpoint is the token exchange endpoint, which is used to obtain encrypted strings, called tokens, that authorize a user to access your service.

When a Google application needs to call one of your service's APIs, Google uses these endpoints together to get permission from your users to call these APIs on their behalf.

An OAuth 2.0 authorization code flow session initiated by Google has the following flow:

1. Google opens your authorization endpoint in the user's browser. If the flow started on a voice-only device for an Action, Google transfers the execution to a phone.
2. 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.
3. Your service creates an authorization code and returns it to Google. To do so, redirect the user's browser back to Google with the authorization code attached to the request.
4. Google sends the authorization code to your token exchange endpoint, which verifies the authenticity of the code and returns an access token and a refresh token. The access token is a short-lived token that your service accepts as credentials to access APIs. The refresh token is a long-lived token that Google can store and use to acquire new access tokens when they expire.
5. After the user has completed the account linking flow, every subsequent request sent from Google contains an access token.

Handle authorization requests

When you need to perform account linking using the OAuth 2.0 authorization code 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&scope=REQUESTED_SCOPES&response_type=code

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

1. Verify that the client_id matches the Client ID you assigned to Google, and that the redirect_uri matches the redirect URL provided by Google for your service. These checks are important to prevent granting access to unintended or misconfigured client apps. If you support multiple OAuth 2.0 flows, also confirm that the response_type is code.
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 authorization code for Google to use to access your API. The authorization code can be any string value, but it must uniquely represent the user, the client the token is for, and the code's expiration time, and it must not be guessable. You typically issue authorization codes that expire after approximately 10 minutes.
4. 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
     

5. Redirect the user's browser to the URL specified by the redirect_uri parameter. Include the authorization code you just generated and the original, unmodified state value when you redirect by appending the code and state parameters. The following is an example of the resulting URL:

   https://oauth-redirect.googleusercontent.com/r/YOUR_PROJECT_ID?code=AUTHORIZATION_CODE&state=STATE_STRING

Handle token exchange requests

Your service's token exchange endpoint is responsible for two kinds of token exchanges:

• Exchange authorization codes for access tokens and refresh tokens
• Exchange refresh tokens for access tokens

Token exchange requests include the following parameters:

Configure how Google sends credentials to your server

Depending on its implementation, your authorization server expects to receive client credentials either in the request body, or in the request header.

By default, Google sends the credentials in the request body. If your authorization server requires the client credentials to be in the request header, you must configure your Cloud-to-cloud integration accordingly:

Go to the Developer Console

1. From the list of projects, click Open next to the project you want to work with.

2. Under Cloud-to-Cloud, select Develop.

3. Click Open next your integration.

4. Scroll down to the Permissions (optional) section and select the Have Google transmit Client ID and secret via HTTP basic auth header checkbox.

5. Click Save to save your changes.

Exchange authorization codes for access tokens and refresh tokens

After the user signs in and your authorization endpoint returns a short-lived authorization code to Google, Google sends a request to your token exchange endpoint to exchange the authorization code for an access token and a refresh token.

For these requests, the value of grant_type is authorization_code, and the value of code is the value of the authorization code you previously granted to Google. The following is an example of a request to exchange an authorization code for an access token and a refresh token:

POST /token HTTP/1.1
Host: oauth2.example.com
Content-Type: application/x-www-form-urlencoded

client_id=GOOGLE_CLIENT_ID&client_secret=GOOGLE_CLIENT_SECRET&grant_type=authorization_code&code=AUTHORIZATION_CODE&redirect_uri=REDIRECT_URI

To exchange authorization codes for an access token and a refresh token, your token exchange endpoint responds to POST requests by executing the following steps:

1. Verify that the client_id identifies the request origin as an authorized origin, and that the client_secret matches the expected value.
2. Verify that the authorization code is valid and not expired, and that the client ID specified in the request matches the client ID associated with the authorization code.
3. Confirm that the URL specified by the redirect_uri parameter is identical to the value used in the initial authorization request.
4. If you can't verify all of the above criteria, return an HTTP 400 Bad Request error with {"error": "invalid_grant"} as the body.
5. Otherwise, use the user ID from the authorization code to generate a refresh token and an access token. These tokens can be any string value, but they must uniquely represent the user and the client the token is for, and they must not be guessable. For access tokens, also record the expiration time of the token, which is typically an hour after you issue the token. Refresh tokens don't expire.
6. Return the following JSON object in the body of the HTTPS response:

   {
   "token_type": "Bearer",
   "access_token": "ACCESS_TOKEN",
   "refresh_token": "REFRESH_TOKEN",
   "expires_in": SECONDS_TO_EXPIRATION
   }

Google stores the access token and the refresh token for the user and records the expiration of the access token. When the access token expires, Google uses the refresh token to get a new access token from your token exchange endpoint.

Exchange refresh tokens for access tokens

When an access token expires, Google sends a request to your token exchange endpoint to exchange a refresh token for a new access token.

For these requests, the value of grant_type is refresh_token, and the value of refresh_token is the value of the refresh token you previously granted to Google. The following is an example of a request to exchange a refresh token for an access token:

POST /token HTTP/1.1
Host: oauth2.example.com
Content-Type: application/x-www-form-urlencoded

client_id=GOOGLE_CLIENT_ID&client_secret=GOOGLE_CLIENT_SECRET&grant_type=refresh_token&refresh_token=REFRESH_TOKEN

To exchange a refresh token for an access token, your token exchange endpoint responds to POST requests by executing the following steps:

1. Verify that the client_id identifies the request origin as Google, and that the client_secret matches the expected value.
2. Verify that the refresh token is valid, and that the client ID specified in the request matches the client ID associated with the refresh token.
3. If you can't verify all of the above criteria, return an HTTP 400 Bad Request error with {"error": "invalid_grant"} as the body.
4. Otherwise, use the user ID from the refresh token to generate an access token. These tokens can be any string value, but they must uniquely represent the user and the client the token is for, and they must not be guessable. For access tokens, also record the expiration time of the token, typically an hour after you issue the token.
5. Return the following JSON object in the body of the HTTPS response:

   {
   "token_type": "Bearer",
   "access_token": "ACCESS_TOKEN",
   "expires_in": SECONDS_TO_EXPIRATION
   }

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.