I have an app in google engine with a go backend. I'm trying to retrieve a json file that I previously saved in google cloud storage. The backend is based on polymer and javascript. The problem is that the data need to be retrieved using the user-id through a core-ajax call.

Here is the javascript code I'm using at the moment:

```
loadTrials : function loadTrials() {
            var _this = this,
                load = this.shadowRoot.querySelector('#load-trial');

            load.url="http://url/loadTrials";
            load.go();
            load.addEventListener('core-response', function(ev) {
                var json = ev.detail.response;
                _this.trialData = JSON.parse(json)['trial-data'];
                console.log(JSON.parse(json)['trial-data'])
            }, false);
        }

```

The HTML

```
<core-ajax id="load-trial"  method="GET"></core-ajax>

```

And the backend in go(just the relevant part):

```
func handleloadTrials(w http.ResponseWriter, r *http.Request) {

    defer r.Body.Close()

    //retrieve trials
    http.ServeFile(w, r, JSON file related to user id)

}

```

I know this code is wrong, but I'm completely stuck and I don't know how to pass the user ID to the GET method, and then use the ID to retrieve the specific file on cloud storage (it's a json file) and then pass this Json file to the http.ServeFile method in Go.

Any help?
Thanks a lot.