query-params are added by https://github.com/metosin/reitit/blob/master/modules/reitit-middleware/src/reitit/ring/middleware/parameters.clj middleware, and body-params are added by https://github.com/metosin/reitit/blob/master/modules/reitit-middleware/src/reitit/ring/middleware/muuntaja.clj#L58 middleware 🙂 You can see in https://github.com/metosin/reitit/blob/master/examples/ring-spec-swagger/src/example/server.clj#L86 example how they are added

It's perhaps also worth noting that query-params can come from the https://github.com/ring-clojure/ring/blob/1.7.0/ring-core/src/ring/middleware/params.clj#L48 that does the same. You don't have to use the reitit middlewares, but they are data-driven so they play nicely with the middleware chain.

It's the same with body-params. We have our own middleware that handles JSON parsing (i.e. we're not using muuntaja for historical reasons), but we inject the data into :body-params so that we can leverage reitit coercion to inspect and coerce the data therein

It's really up to you!