How to pointing a radius server paramenter to make external authentication from users in a mesh networks into openwrt

People i am trying to configure a way that users in our mesh network can authenticate in a external capitive portal, but the problem is that everyone that goes out through the wan port in the router with libremesh (lede 17.06) to the server with pfsense with capitive portal, goes out with the mac of this WAN port, in resume, the fisrt user that make the login in capitive portal, make free the usage of the internet into the mesh for everyone that connects after the first user.
How can i configure this wan to make transparent the mac address of the user in the mesh that are going to this port to access the internet ? thks. marcelo