Unlocking Google’s Full API Universe and Authentication Flows in Google Apps Script

A Google Apps Script project that dynamically generates modern, feature-rich client libraries for any public Google API directly from the Google API Discovery Service.

For many developers, Google Apps Script is the go-to platform for rapidly automating and extending Google Workspace. Its simplicity and deep integration are powerful. But as projects grow in ambition, developers often encounter two significant walls: needing to connect to a Google API that isn’t built-in, or requiring an authentication flow, like a service account, that the standard services don’t support.

What if you could break through those walls? What if you could use a robust client library for almost any Google API—from Firebase to Cloud Billing—in seconds, right from Apps Script itself?

Today, I’m excited to introduce the Google API Client Library Generator for Apps Script, a project and code repository designed to solve these very challenges. It comes with a full suite of pre-built libraries, enabling you to significantly expand what’s possible on the platform.

Why This Matters: Beyond the Built-in Services

While Apps Script’s built-in and advanced services are excellent, they represent just a fraction of Google’s vast API ecosystem. This collection of generated libraries unlocks the rest, offering two critical advantages:

1. Complete API Coverage: The generator uses the Google APIs Discovery Service to create clients for over 400 APIs. If it’s in the Google Discovery Service then there is a library for it in the repository.
2. Flexible Authentication Flows: Generated libraries are not tied to the standard user-permission model. This means you can use service accounts for server-to-server authentication, or implement other OAuth2 flows as needed.

Getting Started

Getting started is as simple as finding the library you need in the build/ directory of the GitHub repository and copying the code into your Apps Script project. For detailed setup instructions and other authentication options, please refer to the main README.md in the repository.

Unlocking Professional Workflows with Service Accounts

The real power of this approach comes from flexible authentication. For Google Workspace developers, this also unlocks the ability to use service accounts with domain-wide delegation to make API calls on behalf of other users in your domain.

To handle the authentication flow, you’ll need an OAuth2 library. The following example uses the OAuth2 for Apps Script library, but other options are also available. Once you have your chosen library set up, you can use the following pattern:

// The email of the user to impersonate (for domain-wide delegation).
const USER_EMAIL = '[email protected]'; 

function getService_() {
  // Credentials from the service account's JSON key file.
  const serviceAccountCreds = {
    "private_key": "-----BEGIN PRIVATE KEY-----\n...",
    "client_email": "[email protected]",
  };

  // Use a unique name for the service, like 'Drive' or 'BigQuery', to avoid
  // token collisions between different services.
  return OAuth2.createService('Drive:' + USER_EMAIL)
      .setTokenUrl('https://oauth2.googleapis.com/token')
      .setPrivateKey(serviceAccountCreds.private_key)
      .setIssuer(serviceAccountCreds.client_email)
      .setSubject(USER_EMAIL)
      .setCache(CacheService.getUserCache())
      .setScope('https://www.googleapis.com/auth/drive');
}

/**
 * Lists files using the configured service account.
 */
function listFilesWithServiceAccount() {
  const service = getService_();
  if (!service.hasAccess()) {
    console.log('Service Account authentication failed: ' + service.getLastError());
    return;
  }
  
  const token = service.getAccessToken();

  // This is where the generated library is used with the custom token.
  const drive = new Drive({
    token: token 
  });

  const files = drive.files.list({
    supportsAllDrives: true,
    pageSize: 10
  });
  
  console.log('Files found via service account:', JSON.stringify(files, null, 2));
}

Under the Bonnet: The Generator

For those who want to tweak the generation logic or integrate it into their own workflows, the generator itself is included in the repository. It’s a self-contained Apps Script project that fetches API metadata and programmatically constructs modern, robust ES6 classes with features like automatic exponential backoff for handling API errors.

Join the Community and Contribute

This project was heavily inspired by the work of Spencer Easton and aims to build upon that foundation. It’s a community effort.

While libraries for all APIs are generated, not all have been extensively tested. If you use a library and find a bug, or have an idea for an improvement, please open a GitHub Issue. Pull requests are, of course, always welcome. Happy scripting!

Source: GitHub – mhawksey/Google-API-Client-Library-Generator-for-Apps-Script