将用户ID传递给核心Ajax方法GET，以检索Google Cloud存储中的数据

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.

I partially solved in this way

Javascript:

loadTrials : function loadTrials() {
            var _this = this,
                load = this.shadowRoot.querySelector('#load-trial');
            //pass userID to core-ajax
            _this.userID = _this.app.userSession.user;
            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);
        }

HTML:

<core-ajax id="load-trial" params="{{userID}}" method="GET"></core-ajax>

Go:

type trialStruct []struct {
    Trial struct {
        Index           int    `json:"index"`
        Word            string `json:"word"`
        WordDisplayTime int    `json:"wordDisplayTime"`
        AnswerMaxTime   int    `json:"answerMaxTime"`
        FixationTime    int    `json:"fixationTime"`
        Train           bool   `json:"train"`
        Test            bool   `json:"test"`
        Grammatical     bool   `json:"grammatical"`
        Grammar         string `json:"grammar"`
        keyboard        bool   `json:"keyboard"`
    }
    Metadata struct {
    }
}

func (d *saveData) readFile(fileName string) trialStruct {
    trialName := fileName + "/trials"
    rc, err := storage.NewReader(d.ctx, bucket, trialName)
    if err != nil {
        d.errorf("readFile: unable to open file from bucket %q, file %q: %v", bucket, trialName, err)

    }
    defer rc.Close()
    slurp, err := ioutil.ReadAll(rc)
    if err != nil {
        d.errorf("readFile: unable to read data from bucket %q, file %q: %v", bucket, fileName, err)
    }
    var trialJson trialStruct
    err1 := json.Unmarshal(slurp, &trialJson)
    if err != nil {
        log.Printf("error:", err1)
    }
    return trialJson
}

But now I have the Encoded Json file which I'm not sure how to send back to the javascript, any help? Thanks

<core-ajax url="{{url}}" handleAs="json" params='{"userID": "{{userID}}"}'></core-ajax>

The parameter should be on JSON format.