This is a troubleshooting note that came about after quite a bit of testing. It seems that the original Drupal module is configured to pass COOKIES via curl. I'm not sure why or what cookies it is passing, but if the cookie becomes large enough, the request will fail with a 400 BAD REQUEST error.

We should consider to remove the following lines from the Drupal module:

$sAllCookies = '';
foreach($_COOKIE as $sKey=>$sValue){
     $sAllCookies .= $sKey."=".$sValue.";";
}
curl_setopt($rConnect, CURLOPT_COOKIE, $sAllCookies);