Add redirect.

lms/static/js/ajax-error.js

+$(document).ajaxError(function (event, jXHR) {
+    if (jXHR.status === 403) {
+        alert(gettext('You\'re logged out. Redirecting on login page.'));
+        window.location = '/accounts/login';
+    }
+});

lms/templates/courseware/courseware.html

@@ -49,6 +49,8 @@ ${page_title_breadcrumbs(course_name())}
   ## codemirror
   <script type="text/javascript" src="${static.url('js/vendor/codemirror-compressed.js')}"></script>
 
+  <script type="text/javascript" src="${static.url('js/ajax-error.js')}"></script>
+
   <%static:js group='courseware'/>
   <%static:js group='discussion'/>