Implementare un server OAuth 2.0

Ogni integrazione di Cloud-to-cloud deve includere un meccanismo per l'autenticazione degli utenti.

L'autenticazione ti consente di collegare gli Account Google dei tuoi utenti con gli account utente nel tuo sistema di autenticazione. In questo modo puoi identificare i tuoi utenti quando il tuo fulfillment riceve un intent per la smart home. Google Home per la smart home supporta solo OAuth con un flusso di codice di autorizzazione.

Questa pagina descrive come configurare il server OAuth 2.0 in modo che funzioni con l'integrazione di Cloud-to-cloud.

Collegamento dell'account Google con OAuth

Nel flusso del codice di autorizzazione, sono necessari due endpoint:

• L'endpoint di autorizzazione, che mostra l'interfaccia utente di accesso agli utenti che non hanno ancora eseguito l'accesso. L'endpoint di autorizzazione crea anche un codice di autorizzazione di breve durata per registrare il consenso degli utenti all'accesso richiesto.

• L'endpoint di scambio di token, che è responsabile di due tipi di scambi:

  1. Scambia un codice di autorizzazione con un token di aggiornamento a lunga durata e un token di accesso a breve durata. Questo scambio avviene quando l'utente segue il flusso di collegamento dell'account.
  2. Scambia un token di aggiornamento di lunga durata con un token di accesso di breve durata. Questo scambio avviene quando Google ha bisogno di un nuovo token di accesso perché quello in suo possesso è scaduto.

Istruzioni sul design

Questa sezione descrive i requisiti e i consigli di progettazione per la schermata utente che ospiti per i flussi di collegamento OAuth. Dopo essere stata chiamata dall'app di Google, la tua piattaforma mostra all'utente una pagina di accesso a Google e una schermata di consenso per il collegamento dell'account. Dopo aver dato il consenso per collegare gli account, l'utente viene reindirizzato all'app di Google.

Requisiti

1. Devi comunicare che l'account dell'utente verrà collegato a Google, non a un prodotto Google specifico come Google Home o l'Assistente Google.
2. Devi avere una dichiarazione di autorizzazione di Google, ad esempio "Accedendo, autorizzi Google a controllare i tuoi dispositivi". Consulta la sezione Autorizzazione controllo dispositivo Google delle Norme per gli sviluppatori di Google Home.
3. Devi aprire la pagina di collegamento OAuth web e assicurarti che gli utenti dispongano di un metodo chiaro per accedere al proprio Account Google, ad esempio campi per il nome utente e la password. Non utilizzare il metodo Google Sign-In (GSI) che consente agli utenti di collegare gli account senza essere reindirizzati alla pagina di collegamento OAuth web. Si tratta di una violazione delle norme di Google.
4. Devi includere almeno uno dei seguenti elementi nella pagina di collegamento OAuth per indicare l'integrazione a cui l'utente si sta collegando:
   • Logo aziendale
   • Nome azienda
   • Nome integrazione
   • Icona dell'app

Consigli

Ti consigliamo di procedere come segue:

1. Visualizza le Norme sulla privacy di Google. Includi un link alle Norme sulla privacy di Google nella schermata per il consenso.

2. Dati da condividere. Utilizza un linguaggio chiaro e conciso per comunicare all'utente quali dati personali richiede Google e perché.

3. Invito all'azione chiaro. Indica un invito all'azione chiaro nella schermata del consenso, ad esempio "Accetta e collega". Questo perché gli utenti devono capire quali dati sono tenuti a condividere con Google per collegare i propri account.

4. Possibilità di annullare. Fornisci agli utenti un modo per tornare indietro o annullare l'operazione se scelgono di non collegare gli account.

5. Procedura di accesso chiara. Assicurati che gli utenti dispongano di un metodo chiaro per accedere al proprio Account Google, ad esempio campi per il nome utente e la password o Accedi con Google.

6. Possibilità di scollegare. Offri agli utenti un meccanismo per scollegare l'account, ad esempio un URL alle impostazioni dell'account sulla tua piattaforma. In alternativa, puoi includere un link all'Account Google in cui gli utenti possono gestire il proprio account collegato.

7. Possibilità di cambiare account utente. Suggerisci un metodo per consentire agli utenti di cambiare i propri account. Ciò è particolarmente utile se gli utenti tendono ad avere più account.

   • Se un utente deve chiudere la schermata del consenso per cambiare account, invia un errore recuperabile a Google in modo che l'utente possa accedere all'account desiderato con il collegamento OAuth.

8. Includi il tuo logo. Mostrare il logo della tua azienda nella schermata del consenso. Utilizza le linee guida di stile per posizionare il logo. Se vuoi mostrare anche il logo di Google, consulta Loghi e marchi.

Flusso del codice di autorizzazione

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.