Add Menu::getPermission() and Menu::setPermission()

Those two functions are required for filtering menu items based on a user's grants.

refs #8720

library/Icinga/Web/Menu.php

@@ -75,6 +75,17 @@ class Menu implements RecursiveIterator
      */
     protected $parent;
 
+    /**
+     * Permission a user is required to have granted to display the menu item
+     *
+     * If a permission is set, authentication is of course required.
+     *
+     * Note that only one required permission can be set yet.
+     *
+     * @var string|null
+     */
+    protected $permission;
+
     /**
      * Create a new menu
      *
@@ -442,15 +453,27 @@ class Menu implements RecursiveIterator
     }
 
     /**
-     * Set required Permissions
+     * Get the permission a user is required to have granted to display the menu item
      *
-     * @param   $permission
+     * @return string|null
+     */
+    public function getPermission()
+    {
+        return $this->permission;
+    }
+
+    /**
+     * Set permission a user is required to have granted to display the menu item
+     *
+     * If a permission is set, authentication is of course required.
+     *
+     * @param   string  $permission
      *
      * @return  $this
      */
-    public function requirePermission($permission)
+    public function setPermission($permission)
     {
-        // Not implemented yet
+        $this->permission = (string) $permission;
         return $this;
     }