Sending credentials with cross-domain posts?

According to Requests with credentials, Firefox will only send credentials along with cross-domain posts if

invocation.withCredentials = "true";

is set… But it doesn't seem like jQuery's Ajax API provides any mechanism for this.

Is there something I've missed? Is there some other way I can do it?

Functionality is supposed to be broken in jQuery 1.5.

Since jQuery 1.5.1 you should use xhrFields param.

$.ajaxSetup({
    type: "POST",
    data: {},
    dataType: 'json',
    xhrFields: {
       withCredentials: true
    },
    crossDomain: true
});

Docs: http://api.jquery.com/jQuery.ajax/

Reported bug: http://bugs.jquery.com/ticket/8146

You can use the beforeSend callback to set additional parameters (The XMLHTTPRequest object is passed to it as its only parameter).

Just so you know, this type of cross-domain request will not work in a normal site scenario and not with any other browser. I don't even know what security limitations FF 3.5 imposes as well, just so you don't beat your head against the wall for nothing:

$.ajax({
    url: 'http://bar.other',
    data: { whatever:'cool' },
    type: 'GET',
    beforeSend: function(xhr){
       xhr.withCredentials = true;
    }
});

One more thing to beware of, is that jQuery is setup to normalize browser differences. You may find that further limitations are imposed by the jQuery library that prohibit this type of functionality.

In jQuery 3 and perhaps earlier versions, the following simpler config also works for individual requests:

$.ajax(
        'https://foo.bar.com,
        {
            dataType: 'json',
            xhrFields: {
                withCredentials: true
            },
            success: successFunc
        }
    );

The full error I was getting in Firefox Dev Tools -> Network tab (in the Security tab for an individual request) was:

An error occurred during a connection to foo.bar.com.SSL peer was unable to negotiate an acceptable set of security parameters.Error code: SSL_ERROR_HANDSHAKE_FAILURE_ALERT