Why is the browser not setting cookies after an AJAX request returns?

Question

I am making an ajax request using $.ajax. The response has the Set-Cookie header set (I've verified this in the Chrome dev tools). However, the browser does not set the cookie after receiving the response! When I navigate to another page within my domain, the cookie is not sent. (Note: I'm not doing any cross-domain ajax requests; the request is in the same domain as the document.)

What am I missing?

EDIT: Here is the code for my ajax request:

$.post('/user/login', JSON.stringify(data));

Here is the request, as shown by the Chrome dev tools:

Request URL:https://192.168.1.154:3000/user/login
Request Method:POST
Status Code:200 OK

Request Headers:
Accept:*/*
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Connection:keep-alive
Content-Length:35
Content-Type:application/x-www-form-urlencoded; charset=UTF-8
DNT:1
Host:192.168.1.154:3000
Origin:https://192.168.1.154:3000
Referer:https://192.168.1.154:3000/
User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.154 Safari/537.36
X-Requested-With:XMLHttpRequest

Form Data:
{"UserId":"blah","Password":"blah"}:

Response:

Response Headers:
Content-Length:15
Content-Type:application/json; charset=UTF-8
Date:Sun, 16 Mar 2014 03:25:24 GMT
Set-Cookie:SessionId=MTM5NDk0MDMyNHxEdi1CQkFFQ180SUFBUkFCRUFBQVRfLUNBQUVHYzNSeWFXNW5EQXNBQ1ZObGMzTnBiMjVKWkFaemRISnBibWNNTGdBc1ZFcDNlU3RKVFdKSGIzQlNXRkkwVjJGNFJ6TlRVSHA0U0ZJd01XRktjMDF1Y1c1b2FGWXJORzV4V1QwPXwWf1tz-2Fy_Y4I6fypCzkMJyYxhgM3LjVHGAlKyrilRg==; HttpOnly

Answer 1

OK, so I finally figured out the problem. It turns out that setting the Path option is important when sending cookies in an AJAX request. If you set Path=/, e.g.:

Set-Cookie:SessionId=foo; Path=/; HttpOnly

...then the browser will set the cookie when you navigate to a different page. Without setting Path, the browser uses the "default" path. Apparently, the default path for a cookie set by an AJAX request is different from the default path used when you navigate to a page directly. I'm using Go/Martini, so on the server-side I do this:

session.Options(session.Options{HttpOnly: true, Path:"/"})

I'd guess that Python/Ruby/etc. have a similar mechanism for setting Path.

See also: cookies problem in PHP and AJAX