How to build a public Google Slides integration: Building the Auth Flow

Hey there, fellow JavaScript devs! Ready to dive into the world of Google Slides integration? Let's focus on the most crucial part: building a rock-solid auth flow. Buckle up, because we're about to make your integration secure and user-friendly in no time.

Introduction

Building a public Google Slides integration is exciting, but let's face it – without proper authorization, it's like leaving your front door wide open. We'll walk through creating a bulletproof auth flow that'll keep your users' data safe and your integration running smoothly.

Prerequisites

Before we jump in, make sure you've got these basics covered:

• A Google Cloud Console project (you've set that up, right?)
• The necessary APIs enabled (Google Slides API, we're looking at you)
• Your Client ID and Client Secret (keep these safe, they're your golden tickets)

Choosing the right OAuth 2.0 flow

You've got two main options here:

1. Authorization Code Flow: Perfect for server-side apps. It's like the VIP entrance – more secure, but requires a bit more setup.
2. Implicit Flow: Ideal for client-side apps. It's the express lane, quicker but slightly less secure.

Choose wisely based on your app's architecture. For this guide, we'll focus on the Authorization Code Flow, but the principles apply to both.

Implementing the Authorization Code Flow

Let's break this down into three easy steps:

Setting up the authorization endpoint

const authUrl = 'https://accounts.google.com/o/oauth2/v2/auth';
const params = new URLSearchParams({
  client_id: YOUR_CLIENT_ID,
  redirect_uri: YOUR_REDIRECT_URI,
  response_type: 'code',
  scope: 'https://www.googleapis.com/auth/presentations'
});

const fullAuthUrl = `${authUrl}?${params.toString()}`;
// Redirect your user to fullAuthUrl

Handling the redirect and token exchange

After the user grants permission, Google will redirect them back to your app with a code. Now, let's exchange that code for an access token:

const tokenUrl = 'https://oauth2.googleapis.com/token';
const response = await fetch(tokenUrl, {
  method: 'POST',
  headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
  body: new URLSearchParams({
    code: AUTH_CODE,
    client_id: YOUR_CLIENT_ID,
    client_secret: YOUR_CLIENT_SECRET,
    redirect_uri: YOUR_REDIRECT_URI,
    grant_type: 'authorization_code'
  })
});

const { access_token, refresh_token } = await response.json();

Storing and refreshing access tokens

Store these tokens securely (please, not in localStorage). When the access token expires, use the refresh token to get a new one:

const refreshResponse = await fetch(tokenUrl, {
  method: 'POST',
  headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
  body: new URLSearchParams({
    refresh_token: STORED_REFRESH_TOKEN,
    client_id: YOUR_CLIENT_ID,
    client_secret: YOUR_CLIENT_SECRET,
    grant_type: 'refresh_token'
  })
});

const { access_token } = await refreshResponse.json();

Securing the integration

Security isn't just a feature, it's a must-have. Here are two key steps:

1. Use a state parameter to prevent CSRF attacks:

const state = generateRandomString();
// Add state to your authorization URL and verify it on redirect

2. Implement PKCE for added security (especially important for mobile and single-page apps):

const codeVerifier = generateRandomString();
const codeChallenge = base64UrlEncode(sha256(codeVerifier));
// Add code_challenge and code_challenge_method to your auth URL
// Use code_verifier when exchanging the auth code for tokens

Handling user sessions

Associate Google accounts with your app's users and store tokens securely on your server. Never expose tokens to the client-side!

Error handling and edge cases

Be prepared for:

• Expired tokens (use refresh flow)
• User-initiated disconnects (clear stored tokens and re-authenticate)

Always gracefully handle errors and provide clear feedback to your users.

Testing the auth flow

Manual testing is crucial:

1. Go through the auth flow as a user
2. Test token refresh
3. Verify error scenarios

Consider setting up automated tests for critical paths, but remember, some aspects of OAuth flows can be tricky to automate.

Conclusion

And there you have it! You've just built a robust auth flow for your Google Slides integration. Remember, security is an ongoing process, so stay updated with the latest best practices.

Next up: start building those awesome features that'll make your integration shine. You've got this!

Happy coding, and may your auth flows always be secure and your tokens never expire (well, they will, but now you know how to handle that)! 🚀