google apps script post basecamp - google-apps-script

Question

I'm trying to make calls to Basecamp's new API through Google Apps Script. GET, I can do. POST, not so much.
Starting with the path
https://basecamp.com/xxxxxxx/api/v1/projects/xxxxxxx/todolists.json
My code:
var headers = {
'User-Agent' : BCuseragent,
'Authorization' : 'Basic ' + Utilities.base64Encode(BCuser + ':' + BCpass),
'Content-Type' : 'application/json',
'Accept' : 'application/json',
'validateHttpsCertificates' : false
}
function getBC(path) {
var url = BCurl + path;
var opt = {
'headers' : headers,
'method' : "GET"
};
var response = UrlFetchApp.fetch(url, opt);
return response;
}
function postBC(path, payload) {
var url = BCurl + path;
var opt = {
'headers' : headers,
'method' : "POST",
'payload' : JSON.stringify(payload)
};
var response = UrlFetchApp.fetch(url, opt);
return response;
}
The payload I'm passing as a parameter:
{name: "foo", description: "bar"}
The getBC function works (200 OK), the postBC function returns a 403 error. Yet I am the owner of the project, and I've used curl and a Chrome REST client to confirm I can in fact POST new todolists to this project with the same authorization.
Obviously, my headers are malformed somewhere, but I can't see how.

Answer 1

This is a quirk of UrlFetchApp. You can't set the Content-Type using the general "headers" parameter, instead you must use the "contentType" parameter.
See the "Advanced Parameters" table here:
https://developers.google.com/apps-script/reference/url-fetch/url-fetch-app#fetch(String,Object)