CORS - Chrome canceling simple GET request - nginx

Question

I'm trying to set up CORS to work with Socket IO in Node. Unfortunately the request keeps getting cancelled by Chrome:
GET https://example.com/zebra/8601/socket.io/1/?key=example123&t=1377831596484 HTTP/1.1
Origin: https://example.io
Referer: https://example.io/example
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/29.0.1547.57 Safari/537.36
If I open up the URL in a new tab, I get a much nicer response:
HTTP/1.1 200 OK
Server: nginx/1.4.1
Date: Fri, 30 Aug 2013 03:00:12 GMT
Content-Type: text/plain; charset=utf-8
Transfer-Encoding: chunked
Connection: keep-alive
Access-Control-Allow-Origin: *
Access-Control-Allow-Credentials: true
Access-Control-Allow-Methods: GET, PUT, POST, OPTIONS
Access-Control-Allow-Headers: Authorization,Content-Type,Accept,Origin,Referer,User-Agent,DNT,Cache-Control,X-Mx-ReqToken,Keep-Alive,X-Requested-With,If-Modified-Since
While it's an actual cross-origin request though, it just fails.
The Nginx config is as follows:
location ~ ^/zebra/(\d+)(?:/(.*))?$ {
add_header Access-Control-Allow-Origin *;
add_header Access-Control-Allow-Credentials true;
add_header Access-Control-Allow-Methods "GET, PUT, POST, OPTIONS";
add_header Access-Control-Allow-Headers "Authorization,Content-Type,Accept,Origin,Referer,User-Agent,DNT,Cache-Control,X-Mx-ReqToken,Keep-Alive,X-Requested-With,If-Modified-Since";
}
How can I configure things to get it working with CORS?

Answer 1

So the solution was to make sure we were configuring this Socket IO setting correctly at the Node JS end:
io.configure(function() {
io.set('origins', '*:*');
});
.. and then not do anything funky with CORS at the Nginx end, at all.
Removing all add_header Access-Control-Allow occurrences from the Nginx config has done the trick.