Accessing ALM via local Javascript REST API - Login Problem

Hi folks,

I just want to access ALM via local written javascript in the browser (IE11, Firefox) via the REST API but I cannot login :-(

Here is my code for requesting the LWSSO cookie via jquery:

var auth = btoa(USER+":"+PASSWORD);

$.ajax({
    type: "POST",
    url: https://alm.xxx.net/qcbin/authentication-point/j_spring_security_check,
    headers: {
        "Authorization": "Basic " + auth
    },
    success : function(data) { },
});

The response header contains:

    https://alm.xxx.net/qcbin/authentication-point/login.jsp;jsessionid=1gfsdk4pn525f1ur55e2x2zzte?login_error

With OTA everything works fine but I want to use the REST API. Can anyone help me?

Best regards

Martin