Integrate FreeRADIUS with an external REST API for authorization and accounting using rlm_rest

Steps

1. Enable the module by symlinking raddb/mods-available/rest into mods-enabled, then set connect_uri to your backend's base URL in the rest {} config block.
2. Configure per-phase sections (authorize, authenticate, accounting, post-auth) each with their own uri (built from connect_uri plus RADIUS attribute expansions like %{User-Name}), method (get/post/put/patch/delete), and body encoding (none, post, or json).
3. For body = json requests, structure the payload as {"<attribute>":{"type":"<type>","value":[...]}} on the way out, and expect responses in the same typed shape, with op controlling how returned attributes are applied (e.g. += for multiple instances from a multi-value array).
4. Reference the module from a virtual server's authorize {}, authenticate {}, accounting {}, or post-auth {} block (or recv Access-Request {} under v4's unlang) so RADIUS requests actually invoke it.
5. Remember FreeRADIUS is the HTTP client here, not a server — your backend must implement the REST endpoints rlm_rest calls out to, not the other way around.