Authenticate to an external database

Hi If someone can help me I'll be very greatful. I have a router with coova-chilli and openwrt, a freeradius virtual server and i have a server with the users database. I need authenticate the users, im trying with the rlm_rest and eap_tls, im in the correct way ? My doubt is because freeradius server not know the users credentials. These ones are stored in an existing database in an external server. Every user need to install a CA ? Thank you.