Setting and Retrieving email signatures using Google Apps Script for a Google Apps for Business/Education Domain

signatures.js

function getSignatureById(id, domain) {
  
  id = id || __userid__;
  domain = domain || __yourdomain.com__;
  
  var requestData = {
    'method': 'GET',
    'contentType': 'application/atom+xml'
  };
  
  requestData['oAuthServiceName'] = 'emailsignatures';
  requestData['oAuthUseToken'] = 'always';
  
  UrlFetchApp.addOAuthService(signatures_oAuth());  
  
  var signature = UrlFetchApp.fetch('https://apps-apis.google.com/a/feeds/emailsettings/2.0/'+domain+'/'+id+'/signature', requestData); //returns XML
}

function setSignatureById(id, domain, signature) {
  
  id = id || 'userid;
  domain = domain || 'yourdomain.com';
  
  var requestData = {
    'method': 'PUT',
    'contentType': 'application/atom+xml',
    'payload': signaturePayload(signature)
  };
  
  requestData['oAuthServiceName'] = 'emailsignatures';
  requestData['oAuthUseToken'] = 'always';
  
  UrlFetchApp.addOAuthService(signatures_oAuth());  
  
  var signature = UrlFetchApp.fetch('https://apps-apis.google.com/a/feeds/emailsettings/2.0/'+domain+'/'+id+'/signature', requestData); //returns XML
}

function signatures_oAuth() {
  var oAuthConfig = UrlFetchApp.addOAuthService('emailsignatures');
  oAuthConfig.setConsumerSecret(UserProperties.getProperty('oAuthConsumerSecret') ); 
  oAuthConfig.setConsumerKey(UserProperties.getProperty('oAuthClientID'));
  oAuthConfig.setRequestTokenUrl('https://www.google.com/accounts/OAuthGetRequestToken?scope=https%3A%2F%2Fapps-apis.google.com%2Fa%2Ffeeds%2Femailsettings%2F');
  oAuthConfig.setAuthorizationUrl('https://www.google.com/accounts/OAuthAuthorizeToken');
  oAuthConfig.setAccessTokenUrl('https://www.google.com/accounts/OAuthGetAccessToken');
  
  return oAuthConfig;
}

function signaturePayload(signature) {
  signature = signature.replace(/&/g, '&amp;').replace(/</g, '&lt;');
  signature = signature.replace(/>/g, '&gt;').replace(/'/g, '&apos;').replace(/"/g, '&quot;');
  
  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>';
  return xml;
}