use CI as micro engine without views folder

I am also noob

how about filterin by IP in htaccess ? or in index.php  check remote IP address.

if u implement ReST API. rest server this library has built in authentication methods. in rest library config u can set valid user that are able to connect to ur engine-ci api
$config['rest_valid_logins'] = ['admin' => '1234'];
or u can set IP whitelist $config['rest_ip_whitelist_enabled'] = FALSE;

if connection is not secure (not https) $config['rest_valid_logins'] = ['admin' => '1234']; is not secure