OAuth2 for Apps Script

OAuth2 for Apps Script is a library for Google Apps Script that provides the ability to create and authorize OAuth2 tokens as well as refresh them when they expire. This library uses Apps Script's new StateTokenBuilder and /usercallback endpoint to handle the redirects.

Setup

This library is already published as an Apps Script, making it easy to include in your project. To add it to your script, do the following in the Apps Script code editor:

Click on the menu item "Resources > Libraries..."
In the "Find a Library" text box, enter the script ID 1B7FSrk5Zi6L1rSxxTDgDEUsPzlukDsi4KGuTMorsTQHhGBzBkMun4iDF and click the "Select" button.
Choose a version in the dropdown box (usually best to pick the latest version).
Click the "Save" button.

Alternatively, you can copy and paste the files in the /dist directory directly into your script project.

Redirect URI

Before you can start authenticating against an OAuth2 provider, you usually need to register your application and retrieve the client ID and secret. Often these registration screens require you to enter a "Redirect URI", which is the URL that users will be redirected to after they've authorized the token. For this library (and the Apps Script functionality in general) the URL will always be in the following format:

https://script.google.com/macros/d/{SCRIPT ID}/usercallback

Where {SCRIPT ID} is the ID of the script that is using this library. You can find your script's ID in the Apps Script code editor by clicking on the menu item "File > Project properties".

Alternatively you can call the service's getRedirectUri() method to view the exact URL that the service will use when performing the OAuth flow:

/**
 * Logs the redict URI to register.
 */
function logRedirectUri() {
  var service = getService();
  Logger.log(service.getRedirectUri());
}

Usage

Using the library to generate an OAuth2 token has the following basic steps.

1. Create the OAuth2 service

The OAuth2Service class contains the configuration information for a given OAuth2 provider, including its endpoints, client IDs and secrets, etc. This information is not persisted to any data store, so you'll need to create this object each time you want to use it. The example below shows how to create a service for the Google Drive API.

function getDriveService() {
  // Create a new service with the given name. The name will be used when
  // persisting the authorized token, so ensure it is unique within the
  // scope of the property store.
  return OAuth2.createService('drive')

      // Set the endpoint URLs, which are the same for all Google services.
      .setAuthorizationBaseUrl('https://accounts.google.com/o/oauth2/auth')
      .setTokenUrl('https://accounts.google.com/o/oauth2/token')

      // Set the client ID and secret, from the Google Developers Console.
      .setClientId('...')
      .setClientSecret('...')

      // Set the name of the callback function in the script referenced
      // above that should be invoked to complete the OAuth flow.
      .setCallbackFunction('authCallback')

      // Set the property store where authorized tokens should be persisted.
      .setPropertyStore(PropertiesService.getUserProperties())

      // Set the scopes to request (space-separated for Google services).
      .setScope('https://www.googleapis.com/auth/drive')

      // Below are Google-specific OAuth2 parameters.

      // Sets the login hint, which will prevent the account chooser screen
      // from being shown to users logged in with multiple accounts.
      .setParam('login_hint', Session.getActiveUser().getEmail())

      // Requests offline access.
      .setParam('access_type', 'offline')

      // Forces the approval prompt every time. This is useful for testing,
      // but not desirable in a production application.
      .setParam('approval_prompt', 'force');
}

2. Direct the user to the authorization URL

Apps Script UI's are not allowed to redirect the user's window to a new URL, so you'll need to present the authorization URL as a link for the user to click. The URL is generated by the service, using the function getAuthorizationUrl().

function showSidebar() {
  var driveService = getDriveService();
  if (!driveService.hasAccess()) {
    var authorizationUrl = driveService.getAuthorizationUrl();
    var template = HtmlService.createTemplate(
        '<a href="<?= authorizationUrl ?>" target="_blank">Authorize</a>. ' +
        'Reopen the sidebar when the authorization is complete.');
    template.authorizationUrl = authorizationUrl;
    var page = template.evaluate();
    DocumentApp.getUi().showSidebar(page);
  } else {
  // ...
  }
}

3. Handle the callback

When the user completes the OAuth2 flow, the callback function you specified for your service will be invoked. This callback function should pass its request object to the service's handleCallback function, and show a message to the user.

function authCallback(request) {
  var driveService = getDriveService();
  var isAuthorized = driveService.handleCallback(request);
  if (isAuthorized) {
    return HtmlService.createHtmlOutput('Success! You can close this tab.');
  } else {
    return HtmlService.createHtmlOutput('Denied. You can close this tab');
  }
}

If the authorization URL was opened by the Apps Script UI (via a link, button, etc) it's possible to automatically close the window/tab using window.top.close(). You can see an example of this in the sample add-on's Callback.html.

4. Get the access token

Now that the service is authorized you can use its access token to make reqests to the API. The access token can be passed along with a UrlFetchApp request in the "Authorization" header.

function makeRequest() {
  var driveService = getDriveService();
  var response = UrlFetchApp.fetch('https://www.googleapis.com/drive/v2/files?maxResults=10', {
    headers: {
      Authorization: 'Bearer ' + driveService.getAccessToken()
    }
  });
  // ...
}

Compatiblity

This library was designed to work with any OAuth2 provider, but because of small differences in how they implement the standard it may be that some APIs aren't compatible. If you find an API that it does't work with, open an issue or fix the problem yourself and make a pull request against the source code.

Other features

Resetting the access token

If you have an access token set and need to remove it from the property store you can remove it with the reset() function. Before you can call reset you need to set the property store.

function clearService(){
  OAuth2.createService('drive')
      .setPropertyStore(PropertiesService.getUserProperties())
      .reset();
}

Setting the token format

OAuth services can return a token in two ways: as JSON or an URL encoded string. You can set which format the token is in with setTokenFormat(tokenFormat). There are two ENUMS to set the mode: TOKEN_FORMAT.FORM_URL_ENCODED and TOKEN_FORMAT.JSON. JSON is set as default if no token format is chosen.

Setting additional token headers

Some services, such as the FitBit API, require you to set an Authorization header on access token requests. The setTokenHeaders() method allows you to pass in a JavaScript object of additional header key/value pairs to be used in these requests.

.setTokenHeaders({
  'Authorization': 'Basic ' + Utilities.base64Encode(CLIENT_ID + ':' + CLIENT_SECRET)
});

See the FitBit sample for the complete code.

Modifying the access token payload

Similar to Setting additional token headers, some services, such as the Smartsheet API, require you to add a hash to the access token request payloads. The setTokenPayloadHandler method allows you to pass in a function to modify the payload of an access token request before the request is sent to the token endpoint:

// Set the handler for modifying the access token request payload:
.setTokenPayloadHandler(myTokenHandler)

See the Smartsheet sample for the complete code.

Service Accounts

This library supports the service account authorization flow, also known as the JSON Web Token (JWT) Profile. This is a two-legged OAuth flow that doesn't require a user to visit a URL and authorize access.

One common use for service accounts with Google APIs is domain-wide delegation. This process allows a Google Apps for Work/EDU domain administrator to grant an application access to all the users within the domain. When the application wishes to access the resources of a particular user, it uses the service account authorization flow to obtain an access token. See the sample GoogleServiceAccount.gs for more information.

Breaking changes

Version 20 - Switched from using project keys to script IDs throughout the library. When upgrading from an older version, ensure the callback URL registered with the OAuth provider is updated to use the format https://script.google.com/macros/d/{SCRIPT ID}/usercallback.

wulftone/apps-script-oauth2