I have a page loading up in MobileSafari which communicated with another server via CORS.
In desktop browsers (tested Chrome and Safari), I am able to log in, get a session cookie, and have that session cookie be sent back for subsequent requests so that I may be authenticated with all API calls.
However, when I login via Mobile Safari, the cookie does not get sent back on subsequent requests.
I'm using Charles Proxy to spy on what's going on, and it tells me:
POST https://myremoteserver.com/sessions.jsonpasses up my login info- It succeeds and response is received with a valid 
Set-Cookieheader. GET https://myremoteserver.com/checkout.jsonis requested, without aCookierequest header.- Server responds as if I am not logged in.
 
I'm using this snippet with Zepto.js to ensure that the withCredentials: true is properly setup on the XHR object. (pardon the coffeescript)
# Add withCredentials:true to the xhr object to send the remote server our cookies.
xhrFactory = $.ajaxSettings.xhr
$.ajaxSettings.xhr = ->
  xhr = xhrFactory.apply(this, arguments)
  xhr.withCredentials = yes
  xhr
And that snippet works great in desktop browsers, and before I added it I was not able to preserve the session cookies in those desktop browsers.
Is there some quirk in MobileSafari that prevents this from working like desktop browsers? Why does it not work in the same way?
Edit!
here is my CORS headers setup in my rails 2.3 app, fairly standard stuff I believe
def add_cors_headers
  if valid_cors_domain
    headers['Access-Control-Allow-Origin']      = request.headers['HTTP_ORIGIN']
    headers['Access-Control-Expose-Headers']    = 'ETag'
    headers['Access-Control-Allow-Methods']     = 'GET, POST, PATCH, PUT, DELETE, OPTIONS, HEAD'
    headers['Access-Control-Allow-Headers']     = '*,x-requested-with,Content-Type,If-Modified-Since,If-None-Match'
    headers['Access-Control-Allow-Credentials'] = 'true'
    headers['Access-Control-Max-Age']           = '86400'
  end
end
Also today desktop Safari on Mountain Lion started not to send the cookie, behaving just like MobileSafari. I'm not entirely sure if my assessment yesterday was inaccurate, or perhaps Apple is just trolling me...
Also could this be affected by using https:// at the remote url?