You can use [[jlogin_form]] shortcode to show the login form if the user is not logged-in. Then you can use the shortcode [fm_access group='logged-in']] to show the filemanager window if the user is logged-in.
You can add these shortcodes to any page where you want to show a login page and the filemanager window.


[[jlogin_form]]
[[fm_access group='logged-in']
[filemanager foldername="*"]
[/fm_access]


I added it in the filemanager sample page on your site for you to try it out:

If you’re not logged-in, you will see the login form:

Otherwise you’ll see the filemanager window: