Steps to reproduce

Set a server with proxy host as proxy.example.org and final to final.example.org
Set your config like someting like this

     'session' => array (
        'sessionName'=>'LS-dqsdqsE',
        'cookieParams' => array(
            'domain' => "final.example.org",
        ),
     ),
    'request' => array(
        'csrfCookie' => array( 
            'domain' => 'final.example.org',
        ),
    ),

(Lime survey work without this , but not kcfinder)
Test
Expected result

Cookies was created and browse work

Actual result

Cookies was not created, browse doidn't work (and receive console error)