Gmail Signature using apps scripts, Gmail API and a G Suite Domain

README.md

Gmail signature using GMail API and G Suite domain

code.gs

// Original code : https://stackoverflow.com/a/40936258/11379030
function setSignatureTest() {
  var user = {
    primaryEmail: "name@example.com",
    name: {
      fullName:'First Last',
      familyName:'Last name',
      givenName:'First name'
    }
  };
  var test = setSignature(user.primaryEmail, user);

  Logger.log('test result: ' + test);

}

function listAllUsers() {
  var pageToken;
  var page;
  do {
    page = AdminDirectory.Users.list({
      domain: 'example.com',
      orderBy: 'givenName',
      maxResults: 500,
      pageToken: pageToken
    });
    var users = page.users;

    var accountsToIgnore = [
      'test@example.com',
      'testtest@example.com'
    ];

    if (users) {
      for (var i = 0; i < users.length; i++) {
        var user = users[i];
        if (accountsToIgnore.indexOf(user.primaryEmail) == -1) {
          var userName = user.name.fullName;
          var userEmail = user.primaryEmail;
          var userOrgRole = user.organizations ? user.organizations[0].title : ''
          Logger.log('-- %s (%s) %s', userName, userEmail, userOrgRole);
          Logger.log('%s (%s)', user);
          setSignature(userEmail, user);
        }

      }
    } else {
      Logger.log('No users found.');
    }
    pageToken = page.nextPageToken;
  } while (pageToken);
}

function setSignature(email, userData) {
  var signatureSetSuccessfully = false;
  var authorizationScope = ['https://www.googleapis.com/auth/gmail.settings.sharing','https://www.googleapis.com/auth/gmail.settings.basic'];
  
  var service = getDomainWideDelegationService("Gmail: ", authorizationScope, email);

  if (!service.hasAccess()) {
    Logger.log("failed to authenticate as user " + email);
    Logger.log(service.getLastError());

    signatureSetSuccessfully = service.getLastError();

    return signatureSetSuccessfully;
  } else {
    Logger.log("successfully authenticated as user " + email);
  }
  
  var signatureTemplate = HtmlService.createHtmlOutputFromFile("signature").getContent();
  var userSig = signatureTemplate
          .replace(/(\r\n|\n|\r)/gm, "")
          .replace(/{email}/g, userData.primaryEmail)
          .replace(/{firstName}/g, userData.name.givenName)
          .replace(/{lastName}/g, userData.name.familyName)
          .replace(/{jobTitle}/g, userData.organizations ? userData.organizations[0].title : '')
  var resource = { signature: userSig };
  
  var requestBody                = {};
  requestBody.headers            = {"Authorization": "Bearer " + service.getAccessToken()};
  requestBody.contentType        = "application/json";
  requestBody.method             = "PUT";
  requestBody.payload            = JSON.stringify(resource);
  requestBody.muteHttpExceptions = false;

  var emailForUrl = encodeURIComponent(email);

  var url = "https://www.googleapis.com/gmail/v1/users/me/settings/sendAs/" + emailForUrl;

  try {
    var setSignatureResponse = UrlFetchApp.fetch(url, requestBody);
    signatureSetSuccessfully = true;
    Logger.log("setSignatureResponse on successful attempt:" + JSON.parse(setSignatureResponse).sendAsEmail);
  } catch (e) {
    Logger.log("Set signature with HTTP request failed: " + e);
  }
  
  return signatureSetSuccessfully;
}

// these two things are included in the .JSON file that you download when creating the service account and service account key
var OAUTH2_SERVICE_ACCOUNT_PRIVATE_KEY  = '-----BEGIN PRIVATE KEY-----\n\n-----END PRIVATE KEY-----\n';
var OAUTH2_SERVICE_ACCOUNT_CLIENT_EMAIL = 'xxx@yyy.iam.gserviceaccount.com';


function getDomainWideDelegationService(serviceName, scope, email) {

  Logger.log('starting getDomainWideDelegationService for email: ' + email);

  return OAuth2.createService(serviceName + email)
      // Set the endpoint URL.
      .setTokenUrl('https://accounts.google.com/o/oauth2/token')

      // Set the private key and issuer.
      .setPrivateKey(OAUTH2_SERVICE_ACCOUNT_PRIVATE_KEY)
      .setIssuer(OAUTH2_SERVICE_ACCOUNT_CLIENT_EMAIL)

      // Set the name of the user to impersonate. This will only work for
      // Google Apps for Work/EDU accounts whose admin has setup domain-wide
      // delegation:
      // https://developers.google.com/identity/protocols/OAuth2ServiceAccount#delegatingauthority
      .setSubject(email)

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

      // Set the scope. This must match one of the scopes configured during the
      // setup of domain-wide delegation.
      .setScope(scope);

}

IT WORKS, thank you, I have a question... Is there a way to update a signature? It only works when I do not have any signature registered