The return value from SimpleSAML\Utils\HTTP::fetch() can never be false.

If something fails, an exception would be thrown, instead of “false” being returned.

Also, at this point we are sure that the return value will be a string, because the call to fetch() does not set the third parameter ($getHeaders) to true.

lib/SimpleSAML/Bindings/Shib13/Artifact.php

@@ -179,10 +179,7 @@ class Artifact
 
         // Fetch the artifact
         $response = HTTP::fetch($url, $opts);
-        if ($response === false) {
-            throw new \SimpleSAML_Error_Exception('Failed to retrieve assertion from IdP.');
-        }
-
+        /** @var string $response */
         XML::debugSAMLMessage($response, 'in');
 
         // Find the response in the SOAP message