events.cljs

(rf/reg-event-fx
 :auth
 (fn [{:keys [db]} _]
   {:POST
    {:url "https://api.intra.42.fr/oauth/token"
     :on-success [:auth/response-received]
     :on-fail :auth-nok
     :params
     {:grant_type "client_credentials"
      :client_id "secret"
      :client_secret "secret"}}}))

;; Separate event handler has access to the db and the response
(rf/reg-event-db
 :auth/response-received
 (fn [db [_ resp]]
   (assoc db :token (get resp :access_token)))