Pass REMOTE_USER to the backend

We would like to pass `REMOTE_USER` to the backend and use it for authentication.

`REMOTE_USER` is added because it was not included in the target to be passed.
It is passed to the backend with the ` X-Forwarded-User` header.

Author: abetomo

no.php

@@ -68,6 +68,8 @@ function getRequestHeaders($multipart_delimiter=NULL) {
                 // Handle application/json
                 array_push($headers, "$key: $value");
             }
+        } elseif ($key === 'REMOTE_USER') {
+            array_push($headers, "X-Forwarded-User: $value");
         }
     }
     return $headers;