If you are using Pfsense Firewall as an OpenVPN endpoint, then chances are, you are aware that you can authenticate your users against multiple types of authentication providers. Beyond that, you can also use authentication providers to allow access to the administration interface of Pfsense itself. In this tutorial I will show you how to configure Samba4 as a Pfsense authentication provider. First you need to navigate to System > User Manager. Once there you will want to be on the Servers tab as seen below. 
Now Click on the + sign seen above circled in red. That will open the page pictured below which will allow you to add your provider. Fill in the textboxes as seen below, obviously using your servers information. Once complete, hit save and head over to Diagnostics > Authentication to test your Samba4 authentication provider.
Input your credentials and click test. If you see an image like the one below, then your authentication provider is working as it is supposed to. Now your new provider will be available Pfsense wide to be used for authentication.