I don't believe Zapier will allow that, specifically.
Here's an alternative that may work perfectly: Put the GET in the step 3 script and use fetch!
Here's an example:
//Put in your url with querystring
var url = "https://somewhere.com/rest?para1=value1";
//Add the method and headers here
fetch(url, {method: "GET", headers: {"Content-Type": "application/json"}})
.then(function (response) {
console.log(response);
return response.json();
}).then(function (data) {
//This is the entire JSON. Put your code here
// Remember to do a callback! Do not set to "output"
console.log(data);
//This will return data as output
callback(null, data);
});
//Code here will execute BEFORE code within the then functions because it's asynchronus
See this link for more on fetch: https://github.com/bitinn/node-fetch/tree/32b60634434a63865ea3f79edb33d17e40876c9f#usage
Hope this helps!