Encode image into URL parameter node.js

I'm attempting to send information to an external API. To quote their support:

"The file should be encoded in Base64 and inserted into the image parameter. "

I'm not sure if I'm misunderstanding something fundamental, but I am getting a 414-URI Too Large when I try to do so.

I wrote a short node.js script to do it:

var fs = require('fs');
var request = require('request');

var host = "api.xxxxx.com";
var app_id = "xxxxxxxx";
var app_key = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
var sessionID = null;

function base64_encode(filename) {
    // read binary data
    var data = fs.readFileSync('./images/' + filename);
    // convert binary data to base 64 encoded string
    return new Buffer(data).toString('base64');
}

function start() {
    fs.readdir('./images/', function(err, files) {
        if (err) {
            console.log("Error in fs.readdir: ", err);
        }
        else {
            files.forEach(function(file) {
                var base = base64_encode(file);
                request.post({
                    url: 'https://api.xxxxxxx.com/media?source=' + base,
                    headers: {
                        'app_id': app_id,
                        'app_key': app_key
                    }}, function (error, response, body) {
                    if (response) {
                        console.log('Status:', response.statusCode);
                        console.log('Headers:', JSON.stringify(response.headers));
                        console.log('Response:', body);
                    }
                    else {
                        console.log("No response.");
                    }
                });
            });
        }
    })
}

start();

I've also tried putting the encoded image in form: {}, qs: {}, and moved it basically all over the place - i either get a "Required source parameter missing" error, or if I seem to get it right, I get the 414. Any advice on sending an image this way? It is a 144KB image.

Edit:

I changed the meat of the code to this:

        files.forEach(function(file) {
            var data = base64_encode(file);
            var options = {
                host: host,
                port: 443,
                path: '/media',
                method: 'POST',
                headers: {
                    'app_id': app_id,
                    'app_key': app_key,
                    'Content-Type': 'image/jpg',
                    'Content-Length': data.length   
                }

            };
            var req = https.request(options, function(res) {
                res.setEncoding('utf8');
                res.on('data', function (chunk) {
                    console.log("body: " + chunk);
                });
            });
            req.write(data);
            req.end();
        });

But I am still getting "required source parameter missing" as a response. How do I specify it as the "source" parameter?