fix forwarded headers

Author: coolya

server/src/main/kotlin/cloud/skadi/gist/plugins/HTTP.kt

@@ -25,7 +25,10 @@ fun Application.configureHTTP() {
         }
     }
     install(ForwardedHeaderSupport) // WARNING: for security, do not include this if not behind a reverse proxy
-    install(XForwardedHeaderSupport) // WARNING: for security, do not include this if not behind a reverse proxy
+    install(XForwardedHeaderSupport) {
+        this.hostHeaders.clear()
+        this.hostHeaders.add(HttpHeaders.XForwardedHost)
+    }
     install(ContentNegotiation) {
         jackson()
     }