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Google-Kontoverknüpfung mit OAuth

Konten werden über die branchenüblichen impliziten und Autorisierungscode-Vorgänge für OAuth 2.0 verknüpft. Ihr Dienst muss OAuth 2.0-konforme Autorisierungs- und Token-Austauschendpunkte unterstützen.

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:
1. 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.
2. 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.

Design guidelines

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.

This figure shows the steps for a user to link their Google account
to your authentication system. The first screenshot shows
user-initiated linking from your platform. The second image shows
user sign-in to Google, while the third shows the user consent and
confirmation for linking their Google account with your app. The
final screenshot shows a successfully linked user account in the
Google app. — **Figure 1.** Account linking user sign in to Google and consent screens.

Requirements

You must communicate that the user’s account will be linked to Google, not a specific Google product like Google Home or Google Assistant.

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.
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.

Projekt erstellen

So erstellen Sie Ihr Projekt für die Kontoverknüpfung:

Klicken Sie auf Projekt erstellen.
Geben Sie einen Namen ein oder übernehmen Sie den generierten Vorschlag.
Bestätigen oder bearbeiten Sie die verbleibenden Felder.
Klicken Sie auf Erstellen.

So rufen Sie Ihre Projekt-ID auf:

Suchen Sie in der Tabelle auf der Landingpage nach Ihrem Projekt. Die Projekt-ID wird in der Spalte ID angezeigt.

OAuth-Zustimmungsbildschirm konfigurieren

Der Prozess zur Verknüpfung von Google-Konten umfasst einen Zustimmungsbildschirm, auf dem Nutzer darüber informiert werden, welche Anwendung Zugriff auf ihre Daten anfordert, welche Art von Daten angefordert wird und welche Nutzungsbedingungen gelten. Sie müssen den OAuth-Zustimmungsbildschirm konfigurieren, bevor Sie eine Google API-Client-ID generieren.

Öffnen Sie in der Google APIs Console die Seite OAuth-Zustimmungsbildschirm.
Wählen Sie bei Aufforderung das Projekt aus, das Sie gerade erstellt haben.
Füllen Sie auf der Seite „OAuth-Zustimmungsbildschirm“ das Formular aus und klicken Sie auf die Schaltfläche „Speichern“.

Anwendungsname:Der Name der Anwendung, die um Einwilligung bittet. Der Name sollte Ihre Anwendung korrekt widerspiegeln und mit dem Anwendungsnamen übereinstimmen, den Nutzer an anderer Stelle sehen. Der Anwendungsname wird auf dem Zustimmungsbildschirm für die Kontoverknüpfung angezeigt.

Anwendungslogo:Ein Bild auf dem Zustimmungsbildschirm, das Nutzern hilft, Ihre App zu erkennen. Das Logo wird auf dem Zustimmungsbildschirm für die Kontoverknüpfung und in den Kontoeinstellungen angezeigt.

Support-E-Mail-Adresse:Für Nutzer, die Sie wegen Fragen zu ihrer Einwilligung kontaktieren möchten.

Bereiche für Google-APIs:Mit Bereichen kann Ihre Anwendung auf die privaten Google-Daten Ihrer Nutzer zugreifen. Für die Verknüpfung von Google-Konten reicht der Standardbereich (email, profile, openid) aus. Sie müssen keine sensiblen Bereiche hinzufügen. Es empfiehlt sich, Bereiche inkrementell anzufordern, wenn der Zugriff erforderlich ist, und nicht im Voraus. Weitere Informationen

Autorisierte Domains:Um Sie und Ihre Nutzer zu schützen, erlaubt Google die Nutzung autorisierter Domains nur Anwendungen, die sich mit OAuth authentifizieren. Die Links Ihrer Anwendungen müssen auf autorisierten Domains gehostet werden. Weitere Informationen

Link zur Startseite der Anwendung:Die Startseite Ihrer Anwendung. Muss auf einer autorisierten Domain gehostet werden.

Link zur Datenschutzerklärung der Anwendung:Wird auf dem Zustimmungsbildschirm für die Google-Kontoverknüpfung angezeigt. Muss auf einer autorisierten Domain gehostet werden.

Link zu den Nutzungsbedingungen der Anwendung (optional): Muss auf einer autorisierten Domain gehostet werden.

Abbildung 1. Zustimmungsbildschirm für die Google-Kontoverknüpfung für die fiktive App „Tunery“
Prüfen Sie den „Überprüfungsstatus“. Wenn Ihre Anwendung überprüft werden muss, klicken Sie auf die Schaltfläche „Zur Überprüfung einreichen“, um sie zur Überprüfung einzureichen. Weitere Informationen finden Sie unter Voraussetzungen für die OAuth-Überprüfung.

OAuth-Server implementieren

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
`client_id`	The client ID you assigned to Google.
`redirect_uri`	The URL to which you send the response to this request.
`state`	A bookkeeping value that is passed back to Google unchanged in the redirect URI.
`response_type`	The type of value to return in the response. For the OAuth 2.0 implicit flow, the response type is always `token`.
`user_locale`	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:

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:

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
```
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_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.

userinfo endpoint request headers
`Authorization header`	The access token of type Bearer.

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:

Extract access token from the Authorization header and return information for the user associated with the access token.
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.

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.

Implementierung validieren

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.