Session Cookies Attributes are not set properly

how to Set the Secure and Domain attributes for the session cookie

and Set the value of the Path attribute to the actual virtual directory path of the application

If the application resides at /myapp/, then verify that the cookie path is set to; path=/myapp/ and not to; path=/.
I set this in config.php
$config['sess_driver'] = 'files';
$config['sess_cookie_name'] = ' myappa';
$config['sess_expiration'] = 7200;
$config['sess_save_path'] = NULL;
$config['sess_match_ip'] = TRUE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = TRUE;

but it will not work properly
.