Emulating form upload with node.js

I'm trying to emulate a form upload with node.js. The reason is because I'm trying to automate some existing code. My node script looks like this:

var boundary = '--123spamulator--'

var options = {
    hostname: 'myawesomewebsite.com',
    port: 80,
    path: '/api/UploadHandler.ashx',
    method: "POST",
    headers: {
        'Content-Type': 'multipart/form-data; boundary=' + boundary,
    }
};

var req = http.request(options, function (res) {
    var data = "";
    res.on("data", function (chunk) {
        data += chunk;
    });
    res.on("end", function (r) {
        console.log("END");
        //callback(); 
    });
    res.on("error", function (err) {
        console.log("POSTERROR (image)");
        console.log(err);
    });
});

req.on("error", function (err) {
    console.log("POSTERROR - 2 (image)");
    console.log(err);
});

var idPart = "\r\n";
idPart += "Content-Disposition: form-data; name='ID'";
idPart += "\r\n\r\n";
idPart += 12345;
idPart += "\r\n" + boundary;

console.log("SENDING:\r\n" + idPart);
req.write(idPart, "utf-8");
req.end();

and the request that gets sent looks like this:

Content-Disposition: form-data; name="Id"

12345
--123spamulator--

But when I try to read ID from my ASP.NET application like so:

var id = context.Request["ID"]

I get null.