Internet Explorer 10 is ignoring XMLHttpRequest 'xhr.withCredentials = true'

Question

I’m currently having an issue with a cross-domain ajax call using IE10 (in IE10 mode, not compatibility).

Situation: I have two domains, http://a and http://b. I have a cookie set for http://b. I am currently on page http://a.

I want to do a CORS request to http://b using XMLHttpRequest (which should work, according to http://blogs.msdn.com/b/ie/archive/2012/02/09/cors-for-xhr-in-ie10.aspx), and include the cookie in the request. The JS is as follows:

var xhr = new XMLHttpRequest();
xhr.open('GET', 'http://b', true);
xhr.withCredentials = true;
xhr.send();

This should ensure that the cookie is attached to the request; however, the Fiddler trace shows that no cookie is attached, and I get 401: Access Denied.

The server is configured to work with CORS, it includes the Access-Control headers:

Access-Control-Allow-Origin: http://a
Access-Control-Allow-Credentials: true

(this should not make any difference, since there is no OPTIONS preflight request, and the first request IE sends is a GET, and the cookie is not present, thus causing a 401).

Furthermore, the JS snippet works fine in both Firefox and Opera.

Answer 1

It's probably the same old IE P3P issue. With IE's default settings, if a cookie is set without a P3P header also present in the response, the cookie is marked as "first-party only". Which means that in a third-party context, such as an iframe or a CORS request, IE will refuse to send the cookie.

To fix it, you need to supply a P3P header when setting the cookies. See http://msdn.microsoft.com/en-us/library/ms537343%28v=vs.85%29.aspx for details.

Update: Link is now dead, but you can see it at the Internet Archive