Can't Get Custom HTTP Header Response from Aja

I do get the response data, but I can't get my custom HTTP header data.

Yes, this is a cross-domain request. I am doing an Ajax request with Javascript. I've tried this with XMLHttpRequest and also jQuery $.ajax. I've done my server settings, I have these set when sending data:

Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: POST, GET

I do get the response data that I want. But I can't get full HTTP header response.

With PHP, I set the following before sending the text response. So I assume that I should get it with getAllResponseHeaders().

header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('My-Own-Test: nodatahere');

But here's what I got.

Content-Type: text/plain; charset=x-user-defined
Cache-Control: must-revalidate, post-check=0, pre-check=0
Expires: 0

It's missing the My-Own-Test. Just for reference sake, here's my Javascript:

var formData = new FormData();
formData.append('username', 'my_username');
formData.append('book_id', 'test password');
var xhr = new XMLHttpRequest();
xhr.open('POST', 'https://mydomain.com/proc.php', true);
xhr.overrideMimeType("text/plain; charset=x-user-defined");
xhr.onload = function(e) { 
    console.log(this.getAllResponseHeaders());
};
xhr.send(formData);

I even tried it with jQuery... same result.

var data_to_send = {
    username: 'my_username',
    password: 'test_password'
};
var ajaxObj;
ajaxObj = $.ajax({
    url: "https://mydomain.com/proc.php",
    data: data_to_send,
    type: "POST", 
    beforeSend: function ( xhr ) {
        xhr.overrideMimeType("text/plain; charset=x-user-defined");
    }
})
.done(function ( data ) {
    console.log( ajaxObj.getAllResponseHeaders()  );
});

Still... no luck.

But if I go through Firebug or Chrome's Developer Tool, I can see that those tools do return full HTTP header information, including Content-Length, Content-Encoding, Vary, X-Powered-By, Set-Cookie, Server, and of course My-Own-Test.

I wanna thank jbl for pointing me to the right SO question. I got it now...

So, OK... the answer. If you ever wanted to set your own HTTP Header information, and then fetch it using cross-domain Ajax, or something like that, here are some extra HTTP Header you should set on your server side, before sending the response text.

header('Access-Control-Allow-Origin: *');
header("Access-Control-Allow-Methods: POST, GET");      
header('Custom-Header: Own-Data');
header('Access-Control-Expose-Headers: Custom-Header');

Example above uses PHP. But use your own language, what ever you use to set them.

When I asked this question, I had all of that except Access-Control-Expose-Headers. After putting that in, my Javascript Ajax can read the content of HTTP Header Custom-Header.