What steps should I take to validate a Google authentication API access token?

Other Questions API
1

I require assistance on how to confirm the validity of a Google authentication access token for a specific account.

Specifically, I need to ascertain whether the access token in question is valid for the user associated with [[email protected]].

### Brief Overview
While it is straightforward to use an access token obtained through Google’s API for data requests from various services, determining the validity of said token for a specific Google account remains unclear to me.

### Detailed Explanation
I am in the process of developing an API that employs token-based authentication. Users can obtain a token either by providing an accurate username and password or through a valid third-party token from a selection of verifiable services. One of these services is Google, allowing users to authenticate to my system with their Google account. In the future, I may also integrate authentication for Yahoo and other trusted OpenID providers.

Here’s a conceptual diagram of how the Google-based access works:

Example Diagram

The ‘API’ is fully managed by me, while the ‘public interface’ can be any web or desktop application, some of which I control and others I don’t. Thus, I cannot fully trust the token that is sent to the API in the third step, which must accompany the relevant Google account email address.

Ultimately, I need a method to ask Google: Is this access token valid for [email protected]? The email is the unique identifier for the Google account and does not necessarily have to be a Gmail address; users can have a Google account without it being linked to Gmail.

According to Google’s documentation, I can retrieve data from various services using an access token, but there is no clear indication on how to check whether a given token is authentic.

### Additional Note
Although I understand that the token works with several Google services, I cannot utilize a Google service as a means of verifying the token since I do not know which specific services a user possesses. My goal is to use the access token purely for validating a user’s identity, and if there are alternative methods to achieve this, I would be open to suggestions.

2

Hey ClimbingLion,

You can validate a Google authentication access token by using Google's OAuth 2.0 token info endpoint. Here’s a quick way to check if the access token is valid for a specific user:

GET https://www.googleapis.com/oauth2/v1/tokeninfo?access_token=ACCESS_TOKEN

Replace ACCESS_TOKEN with the actual token you want to validate. This request will return details about the token.

Check the audience and email fields in the response. Ensure that the email matches [email protected] and audience is aligned with your client ID.

That should do it!

3

To add to Claire29's helpful response, it's good to remember that after you've verified the token information with Google's tokeninfo endpoint, additional precautions can help bolster the security of your authentication system.

One alternative you might explore is the use of Google's OAuth 2.0 libraries, such as the google-auth-library for Node.js if your API is backend-oriented. It encapsulates the entire token validation process using the library's built-in methods, such as the OAuth2Client's verifyIdToken method. By retrieving claims directly, you can ascertain the token’s validity.

const {OAuth2Client} = require('google-auth-library');
const client = new OAuth2Client(CLIENT_ID);

async function verify() {
  const ticket = await client.verifyIdToken({
    idToken: ACCESS_TOKEN,
    audience: CLIENT_ID,  // Specify the CLIENT_ID of the app that accesses the backend
  });
  const payload = ticket.getPayload();
  const userid = payload['sub'];

  // Confirm that the email matches
  if(payload['email'] === '[email protected]') {
    console.log('Token is valid for the user');
  } else {
    console.log('Token is invalid for the user');
  }
}
verify().catch(console.error);

By implementing this in your application, you not only check for token validity but also align with Google's best practices for OAuth 2.0 usage. Additionally, ensuring that all communications are secure with HTTPS and regularly revisiting Google’s API documentation for any updates will further strengthen your system.

4

Hi ClimbingLion,

To validate a Google authentication access token, effectively confirm its validity for a specific user, you can leverage Google's OAuth 2.0 token info endpoint. Here's a straightforward approach:

GET https://www.googleapis.com/oauth2/v1/tokeninfo?access_token=ACCESS_TOKEN

Replace ACCESS_TOKEN with the token you want to validate. The response will provide details of the token, including the associated email and audience.

Follow these steps to ensure the token is valid for [email protected]:

  • Verify the email field in the response to ensure it matches [email protected].
  • Check the audience field to confirm it aligns with your CLIENT_ID.

For enhanced security and efficiency, you might consider using the google-auth-library for Node.js, especially if backend application development is involved. This library simplifies the token validation process with built-in methods. Here's how to use it:

const {OAuth2Client} = require('google-auth-library');
const client = new OAuth2Client(CLIENT_ID);

async function verify() {
  const ticket = await client.verifyIdToken({
    idToken: ACCESS_TOKEN,
    audience: CLIENT_ID,  // YOUR CLIENT_ID
  });
  const payload = ticket.getPayload();

  // Check if the email matches
  if(payload['email'] === '[email protected]') {
    console.log('Token is valid for the user');
  } else {
    console.log('Token is invalid for the user');
  }
}

verify().catch(console.error);

This method not only checks for token validity but also ensures compliance with Google's standards for secure token handling. Don't forget to use HTTPS for all communications to enhance security.

5

Hey ClimbingLion,

For validating a Google access token, use the OAuth 2.0 token info endpoint:

GET https://www.googleapis.com/oauth2/v1/tokeninfo?access_token=ACCESS_TOKEN

Substitute ACCESS_TOKEN with your actual token. Check the response:

  • Ensure the email field matches [email protected].
  • Verify audience matches your CLIENT_ID.

For a programmatic approach, consider using Google’s google-auth-library:

const {OAuth2Client} = require('google-auth-library');
const client = new OAuth2Client(CLIENT_ID);

async function verify() {
  const ticket = await client.verifyIdToken({
    idToken: ACCESS_TOKEN,
    audience: CLIENT_ID,
  });
  const payload = ticket.getPayload();

  if(payload['email'] === '[email protected]') {
    console.log('Token is valid for the user');
  } else {
    console.log('Token is invalid for the user');
  }
}
verify().catch(console.error);
6

To ascertain the validity of a Google access token specifically for a given user, you can indeed utilize the Google OAuth 2.0 token info endpoint, as explained by previous responders. However, I'd like to add another layer of understanding and a distinct approach:

Token Verification Through Introspection:

Sometimes, if detailed introspection information on the token is required, using a token introspection approach might be beneficial. Though Google doesn’t explicitly use OAuth 2.0 introspection, the principle can be applied using existing endpoints for added verification:

GET https://www.googleapis.com/oauth2/v1/tokeninfo?access_token=ACCESS_TOKEN

Replace ACCESS_TOKEN with your token to check. Analyze the response:

  • email: Verify it matches [email protected] to confirm the user.
  • audience: Ensure it aligns with your CLIENT_ID.

Enhance With Google Verification Libraries:

To ensure robust validation, utilizing Google's libraries can leverage pre-built functions that consolidate security checks:

const {OAuth2Client} = require('google-auth-library');
const client = new OAuth2Client(CLIENT_ID);

async function verify() {
  const ticket = await client.verifyIdToken({
    idToken: ACCESS_TOKEN,
    audience: CLIENT_ID,  // Your CLIENT_ID
  });
  const payload = ticket.getPayload();

  if (payload['email'] === '[email protected]') {
    console.log('Token is valid for the user');
  } else {
    console.log('Token is invalid for the user');
  }
}

verify().catch(console.error);

Google’s google-auth-library is particularly useful when integrating Google's OAuth 2.0 into your backend efficiently while maintaining security protocols.

Lastly, ensure your server communicates securely over HTTPS to protect the token during transmission. These methods, combined with regular updates on Google's documentation, will serve to keep your authentication process robust against potential vulnerabilities.