LDAP authentication backend over OpenVPN tunnel

[nikgelfi]

Hi all, we have an OpenVPN site to site tunnel active between two sites
Site A subnet 192.168.0.0/24
Site B subnet 192.168.22.0/24

Both sides run a pfsense 2.7.2 firewall.
On site A firewall, I have created an authentication server (LDAP) pointing to a server which resides in site B. The server is perfectly reachable from any client connected to site A network, but the firewall on site A is not able to contact it.
Is this doable in some manner?
thanks for your help