How to use the Google Email Settings API and the OAuth2 for Apps Script Library to set email signatures for users in a Google Apps domain

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As the administrator of a Google Apps domain, how do you use the Google Email Settings API with OAuth 2 to programmatically set the email signatures of users on your domain in Google Apps Script?

I experienced some confusion when trying to get this to work after OAuth 1 was deprecated, but with some help from awesome SO users, I was able to figure out a working solution.

First, you need to follow the steps to add this library to your Apps Script project:

https://github.com/googlesamples/apps-script-oauth2

After you have that set up, you can use their library to create an OAuth 2 service that is needed when calling the Email Settings API. Here is my working code:

function beginNewEmployeeProcedures() {

  var emailSettingsOauth2Service = createOauth2Service(‘Email Settings API’,’https://apps-apis.google.com/a/feeds/emailsettings/2.0/’,’authCallbackForEmailSettingsApi’);
  if (!emailSettingsOauth2Service.hasAccess()) { startOauth2AuthFlow(‘Email Settings API’,emailSettingsOauth2Service); return; }

  setSignature(emailSettingsOauth2Service,’test@yourgoogleappsdomain.com’,’cool email signature’);

}

function setSignature(service,email,signature) {

  try {

    var username = email.split(“@”)[0];

    var xml = '<?xml version="1.0" encoding="utf-8"?>' +
      '<atom:entry xmlns:atom="http://www.w3.org/2005/Atom" xmlns:apps="http://schemas.google.com/apps/2006" >' +
      '<apps:property name="signature" value="'+ signature +'" /></atom:entry>';

    var fetchArgs = {};
    fetchArgs.headers = {‘Authorization': ‘Bearer ‘+ service.getAccessToken()};
    fetchArgs.method = “PUT”;
    fetchArgs.contentType = “application/atom+xml”;
    fetchArgs.payload = xml;
    fetchArgs.muteHttpExceptions = true;

    var url = ‘https://apps-apis.google.com/a/feeds/emailsettings/2.0/yourgoogleappsdomain.com/’ + username + ‘/signature';

    UrlFetchApp.fetch(url, fetchArgs);

  } catch(e) {

    // failure notification email, etc

  }

}

function createOauth2Service(serviceName,scope,callbackFunctionName) {

  // 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.
  var service = OAuth2.createService(serviceName)

  // 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(OAUTH2_CLIENT_ID)
  .setClientSecret(OAUTH2_CLIENT_SECRET)

  // Set the project key of the script using this library.
  .setProjectKey(OAUTH2_PROJECT_KEY)

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

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

  // Set the scopes to request (space-separated for Google services).
  .setScope(scope)

  // 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’);

  return service;

}

function startOauth2AuthFlow(serviceName,service) {

  var authorizationUrl = service.getAuthorizationUrl();

  var template = HtmlService.createTemplate(
  ‘<a href="” target=”_blank”>’+
  ‘Click here to authorize this script to access the ‘ + serviceName + ‘‘ +
  ‘After closing the other tab, click the X in this window and start the script again.’);

  template.authorizationUrl = authorizationUrl;

  var page = template.evaluate();

  SpreadsheetApp.getUi().showModalDialog(page, ‘API Authorization’);

}

function authCallbackForEmailSettingsApi(request) {

  // this script is called by the auth screen when the user clicks the blue Accept button

  var oauth2Service = createOauth2Service(‘Email Settings API’,’https://apps-apis.google.com/a/feeds/emailsettings/2.0/’,’authCallbackForEmailSettingsApi’);

  var isAuthorized = oauth2Service.handleCallback(request);

  if (isAuthorized) {
    return HtmlService.createHtmlOutput(‘Success! You can close this tab.’);
  } else {
    return HtmlService.createHtmlOutput(‘Didn\’t work.’);
  }

}