Following the Stack Apps documentation Authentication (explicit) section I crafted this AJAX call

        
            $.ajax({
                url:"https://stackexchange.com/oauth/access_token",
                type:"POST",
                data: {
                    client_id: myClientID,
                    client_secret: myClientSecret,
                    code: getUrlParameter("code"),
                    redirect_uri: "https://myapp.com/sameAsBefore" 
                },
                success: function(data){
                    console.log(data);
                }
            });
        
However, this is not accepted. 

> XMLHttpRequest cannot load
> https://stackexchange.com/oauth/access_token. No
> 'Access-Control-Allow-Origin' header is present on the requested
> resource. Origin 'https://myapp.com' is therefore not
> allowed access.

I tried removing the `contentType` and `dataType` as they will default to `application/x-www-form-urlencoded` and a best guess for the returning data. No change if they are there or not.
 
Any ideas what I am missing?