--- lib/ltiprovider/src/OAuth/OAuthRequest.php	2017-11-13 09:35:51.929263025 +0000
+++ lib/ltiprovider/src/OAuth/OAuthRequest.php	2017-11-13 09:37:05.969688574 +0000
@@ -35,7 +35,7 @@
      */
     public static function from_request($http_method = null, $http_url = null, $parameters = null) {
 
-      $scheme = (!isset($_SERVER['HTTPS']) || $_SERVER['HTTPS'] != "on")
+      $scheme = (!isset($_SERVER['HTTPS']) || !$_SERVER['HTTPS'])
                 ? 'http'
                 : 'https';
       $http_url = ($http_url) ? $http_url : $scheme .