FusionAuth doesn't support RADIUS at this time. Please feel free to file a feature request here: https://github.com/fusionauth/fusionauth-issues/issues

We do support LDAP through our connectors, a paid edition feature. More here: https://fusionauth.io/docs/v1/tech/connectors/ldap-connector/

I searched the fusionauth issues list and only came up with one issue mentioning RADIUS, but it may be worth reading if you haven't already. https://github.com/FusionAuth/fusionauth-issues/issues/219