api-call-create-asset.js

var headerNames = ["Authorization"];
var headerValues = ["Bearer " + accessToken];
var jsonBody = {
    "name": fileName,
    "assetType": {
        "name": assetName,
        "id": assetTypeID
    },
    "file": base64enc
};

var requestUrl = rest_instance_url + "asset/v1/content/assets"
var createAsset = HTTP.Post(requestUrl, contentType, Stringify(jsonBody), headerNames, headerValues);