<form name="storeForm" action="{{=return_url}}" method="post" encType="application/x-www-form-urlencoded">
  <input type="hidden" name="lti_message_type" value="ContentItemSelection" />
  <input type="hidden" name="lti_version" value="LTI-1p0" />
  <input type="hidden" name="content_items" value="{{ =assignlist }}" />
  <input type="hidden" name="oauth_version" value="1.0" />
  <input type="hidden" name="oauth_nonce" value="{{ =oauth_nonce}}" />
  <input type="hidden" name="oauth_timestamp" value="{{ =oauth_timestamp }}" />
  <input type="hidden" name="oauth_consumer_key" value="{{=oauth_consumer_key }}" />
  <input type="hidden" name="oauth_callback" value="about:blank" />
  <input type="hidden" name="oauth_signature_method" value="HMAC-SHA1" />
  <input type="hidden" name="oauth_signature" value="{{ =oauth_signature }}" />
</form>

<script type="text/javascript">
    window.onload=function(){
        var auto = setTimeout(function(){ submitform(); }, 1000);

        function submitform(){
            console.log(document.forms["storeForm"]);
            document.forms["storeForm"].submit();
        }
    }
</script>