Ajax jQuery Authentication Request

gistfile1.js

$.ajax( {
	url : '/model/user.json',
	dataType : 'json',
	beforeSend : function(xhr) {
          var bytes = Crypto.charenc.Binary.stringToBytes(username + ":" + password);
          var base64 = Crypto.util.bytesToBase64(bytes);
          xhr.setRequestHeader("Authorization", "Basic " + base64);
	},
	error : function(xhr, ajaxOptions, thrownError) {
	  reset();
	  onError('Invalid username or password. Please try again.');
	  $('#loginform #user_login').focus();
	},
	success : function(model) {
	  cookies();
          ...
	}
});

basic authentication not working..//