Loopback IP Address flow Migration Guide

Overview

On February 16 2022, we announced plans to make Google OAuth interactions safer by using more secure OAuth flows. This guide helps you to understand the necessary changes and steps to successfully migrate from the loopback IP address flow to supported alternatives.

This effort is a protective measure against phishing and app impersonation attacks during interactions with Google's OAuth 2.0 authorization endpoints.

What is the Loopback IP Address flow?

The loopback IP address flow supports the use of a loopback IP address or localhost as the host component of the redirect URI where credentials are sent to after a user approves an OAuth consent request. This flow is vulnerable to man in the middle attacks where a nefarious app, accessing the same loopback interface on some operating systems, may intercept the response from the authorization server to the given redirect URI and gain access to the authorization code.

The loopback IP address flow is being deprecated for the native iOS, Android, and Chrome OAuth client types but will continue to be supported on desktop apps.

Key compliance dates

• March 14, 2022 - new OAuth clients blocked from using the Loopback IP address flow
• August 1, 2022 - a user-facing warning message may be displayed to non-compliant OAuth requests
• August 31, 2022 - the Loopback IP address flow is blocked for native Android, Chrome app, and iOS OAuth clients created before March 14, 2022
• October 21, 2022 - all existing clients are blocked (including exempted clients)

A user-facing error message will be displayed for non-compliant requests. The message will convey to users that the app is blocked while displaying the support email that you have registered in the OAuth consent screen in Google API Console.

Note: If you would like to receive reminders and notifications from Google about this deprecation, make sure you have appropriately configured the contact information for your app by reviewing the support and contact email addresses for your project in the OAuth Consent Screen page of the Google API Console.

There are two main steps to complete to get through the migration process:

1. Determine if you are affected.
2. Migrate to a supported alternative if you are affected.

Determine if you are affected

Review your OAuth client ID type

Navigate to the Credentials page of the Google API Console and view your OAuth client ID type under the OAuth 2.0 Client IDs section. It will be any one of the following: Web application, Android, iOS, Universal Windows Platform (UWP), Chrome app, TVs & Limited Input devices, Desktop app.

Proceed to the next step if your client type is Android, Chrome app, or iOS and you are using the loopback IP address flow.

You do not need to do anything related to this deprecation if you are using the loopback IP address flow on a Desktop app OAuth client as usage with that OAuth client type will continue to be supported.

Note: The deprecation is applicable to the publishing statuses: Testing & In Production and user types: Internal & External.

How to determine if your app is using the loopback IP address flow

Inspect your app code or the outgoing network call (in case your app is using an OAuth library) to determine if the Google OAuth authorization request your app is making is using loopback redirect URI values.

Note: If you are making use of a library to handle your authentication / authorization flows, it is still recommended that you inspect your network call as some libraries abstract the use of the loopback redirect URI values.

Inspect your application code

Review the section of your application code where you are making calls to the Google OAuth authorization endpoints and determine if the redirect_uri parameter has any of the following values:

• redirect_uri=http://127.0.0.1:<port> e.g. redirect_uri=http://127.0.0.1:3000
• redirect_uri=http://[::1]:<port> e.g. redirect_uri=http://[::1]:3000
• redirect_uri=http://localhost:<port> e.g. redirect_uri=http://localhost:3000

A sample loopback IP address redirect flow request will look like the one below:

https://accounts.google.com/o/oauth2/v2/auth?
redirect_uri=http://localhost:3000&
response_type=code&
scope=<SCOPES>&
state=<STATE>&
client_id=<CLIENT_ID>

Note: You should also check your application configuration files (such as .env files) as redirect_uri values are typically set up to be different based on the environment in which the application is running.

Inspect outgoing network call

The method for inspecting network calls will vary depending on your application client type.

• Web application - inspect network activity on Chrome
• Android - inspect network traffic with the Network Inspector
• Chrome apps
  • Navigate to the Chrome extensions page
  • Check the Developer mode checkbox at the top right corner of the extension page
  • Select the extension you want to monitor
  • Click on the background page link in the Inspect views section of the extension page
  • A Developer Tools popup will open up where you can monitor the network traffic in the Network tab
• iOS - Analyzing HTTP traffic with Instruments
• Universal Windows Platform (UWP) - Inspect network traffic in Visual Studio
• Desktop apps - use a network capture tool available for the operating system the app was developed for

While inspecting network calls, look for requests sent to the Google OAuth authorization endpoints and determine if the redirect_uri parameter has any of the following values:

• redirect_uri=http://127.0.0.1:<port> e.g. redirect_uri=http://127.0.0.1:3000
• redirect_uri=http://[::1]:<port> e.g. redirect_uri=http://[::1]:3000
• redirect_uri=http://localhost:<port> e.g. redirect_uri=http://localhost:3000

A sample loopback IP address redirect flow request will look like the one below:

https://accounts.google.com/o/oauth2/v2/auth?
redirect_uri=http://localhost:3000&
response_type=code&
scope=<SCOPES>&
state=<STATE>&
client_id=<CLIENT_ID>

Migrate to a supported alternative

Mobile Clients (Android / iOS)

If you determine that your app is using the loopback IP address flow with an Android or iOS OAuth client type, you should migrate to using our Google Sign-In mobile SDKs (Android, iOS).

The SDK makes it easy to access Google APIs and handles all the calls to Google's OAuth 2.0 authorization endpoints.

The documentation links below provides information on how to use the Google Sign-In SDKs to access Google APIs without using a loopback IP address redirect URI.

Access Google APIs on Android

Server-Side (offline) access

The example below shows how to access Google APIs on the server side on Android.

Note: The server-side (offline) access mode requires you to stand up a server and have a publicly available endpoint to receive the authorization code.

Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);
try {
  GoogleSignInAccount account = task.getResult(ApiException.class);
  
  // request a one-time authorization code that your server exchanges for an
  // access token and sometimes refresh token
  String authCode = account.getServerAuthCode();
  
  // Show signed-in UI
  updateUI(account);

  // TODO(developer): send code to server and exchange for access/refresh/ID tokens
} catch (ApiException e) {
  Log.w(TAG, "Sign-in failed", e);
  updateUI(null);
}

Review the server-side access guide on how to access Google APIs from the server side.

Access Google APIs in an iOS App

Client-side access

The example below shows how to access Google APIs on the client side on iOS.

user.authentication.do { authentication, error in
  guard error == nil else { return }
  guard let authentication = authentication else { return }
  
  // Get the access token to attach it to a REST or gRPC request.
  let accessToken = authentication.accessToken
  
  // Or, get an object that conforms to GTMFetcherAuthorizationProtocol for
  // use with GTMAppAuth and the Google APIs client library.
  let authorizer = authentication.fetcherAuthorizer()
}

Use the access token to call the API, by either including the access token in the header of a REST or gRPC request (Authorization: Bearer ACCESS_TOKEN), or by using the fetcher authorizer (GTMFetcherAuthorizationProtocol) with the Google APIs client library for Objective-C for REST.

Review the client-side access guide on how to access Google APIs on the client side. on how to access Google APIs on the client side.

Server-side (offline) access

The example below shows how to access Google APIs on the server side to support an iOS client.

Note: The server-side (offline) access mode requires you to stand up a server and have a publicly available endpoint to receive the authorization code.

GIDSignIn.sharedInstance.signIn(with: signInConfig, presenting: self) { user, error in
  guard error == nil else { return }
  guard let user = user else { return }
  
  // request a one-time authorization code that your server exchanges for
  // an access token and refresh token
  let authCode = user.serverAuthCode
}

Review the server-side access guide on how to access Google APIs from the server side.

Chrome App Client

If you determine that your app is using the loopback IP address flow on the Chrome app client, you should migrate to using the Chrome Identity API.

The example below shows how to get all user contacts without the use of a loopback IP address redirect URI.

window.onload = function() {
  document.querySelector('button').addEventListener('click', function() {

  
  // retrieve access token
  chrome.identity.getAuthToken({interactive: true}, function(token) {
  
  // ..........


  // the example below shows how to use a retrieved access token with an appropriate scope
  // to call the Google People API contactGroups.get endpoint

  fetch(
    'https://people.googleapis.com/v1/contactGroups/all?maxMembers=20&key=API_KEY',
    init)
    .then((response) => response.json())
    .then(function(data) {
      console.log(data)
    });
   });
 });
};

Review the Chrome Identity API guide for more information on how to access authenticate users and call Google endpoints with the Chrome Identity API.