LDAP Authentication

Hello,

I'm trying to link authentication from /htpassword from nginx to an Active directory.
I'm a bit lost on how to do it.

First, is it possible to do it for free or I have to pay for 'nginx plus'.

I saw this tuto but not clear enough for me :
https://www.nginx.com/blog/nginx-plus-authenticate-users/

Then, how to proceees as I don't find this module :
http://nginx.org/en/docs/http/ngx_http_auth_request_module.html

Many thanks for your help.
Crapoulou.