CakePHP populate checkboxes dynamically

currently i am using CakePHP 2.6 and i have 2 tables and a many to many join table:

 CREATE TABLE IF NOT EXISTS `iam-test_db`.`accesses` (
  `id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
  `location_id` INT UNSIGNED NOT NULL,
  `facility_id` INT UNSIGNED NOT NULL,
  `department_id` INT UNSIGNED NOT NULL,
  PRIMARY KEY (`id`),

 CREATE TABLE IF NOT EXISTS `iam-test_db`.`systems` (
  `id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
  `facility_id` INT UNSIGNED NOT NULL,
  `name` VARCHAR(60) NOT NULL,
  PRIMARY KEY (`id`),
  INDEX `fk_systems_facilities_idx` (`facility_id` ASC),
  CONSTRAINT `fk_systems_facilities`
    FOREIGN KEY (`facility_id`)

CREATE TABLE IF NOT EXISTS `iam-test_db`.`accesses_systems` (
  `id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
  `access_id` INT UNSIGNED NOT NULL,
  `system_id` INT UNSIGNED NOT NULL,
  PRIMARY KEY (`id`),
  CONSTRAINT `fk_accesses_systems_accesses`
    FOREIGN KEY (`access_id`)
  CONSTRAINT `fk_accesses_systems_systems`
    FOREIGN KEY (`system_id`)

I've created succesfully dependent populating dropdowns for facilities and departments and currently listing all systems as checkboxes.

Now i want the checkboxes also be dependent, from which facility i choose. But atm i have no good idea how to make it. I think i have to use javascript/jquery.

I'm thinking about displaying a button and on click a popup window appears with the facility dependent systems. Is this the right way or do you have any better ideas ??

Thanks :-)