Securing a backend

Table of Contents

• Securing a backend
  • Backend with Yada
  • Backend with Ring and Buddy-Auth
  • Backend with Donkey and Buddy-Auth

Prerequisite: The client is correctly configured and is sending with each request either a cookie or a header containing a token. The backend then has to:

1. Extract the token from the cookie or the header of the request (specific to the library used)
2. Verify the token (Keycloak stuff)
3. Ensure the client is accessing the restricted part only if the token is correct (Library specific)

Backend with Yada

Regarding Yada security, read Yada article "Speak friend and Enter!")

The code is in server.clj calling some functions in keycloak.clj.

;;1. Extract the token from the cookie or the header (Yada framework specific)
(defn authorization-token-cookie [ctx]
  (let [cookies (parse-cookies (:request ctx))]
    (get cookies "X-Authorization-Token")))

(defmethod yada.security/verify :keycloak
  [ctx scheme]
  (let [header-cred (authorization-bearer-cred ctx)
        cookie-cred (authorization-token-cookie ctx)]
    (-> (or header-cred cookie-cred)
        ;; Verify the token (Keycloak stuff)
        (keycloak/verify)
        (keycloak/extract))))
        
(defn extract-account-data [ctx]
  (when-let [extracted-token (get-in ctx [:authentication "default"])]
    (let [group-path (.get (get-in extracted-token [:other-claims :group]) 0)]
      {:username (:username extracted-token)
       :group (when group-path (subs group-path (inc (last-index-of group-path "/"))))
       :roles (:roles extracted-token)})))

(defn- restricted-content [ctx]
  (let [account-data (extract-account-data ctx)]
    (html5
     [:body
      [:h1 (format "Hello %s!"
                   (get-in ctx [:authentication "default" :user]))]
      [:p "You're accessing a restricted resource!"]])))

(def routes
  ["/"
   [
    ["hello" ( handler (as-resource "Hello world!"))]
    ["restricted" (resource {:consumes #{"application/json"}
                             :produces {:media-type "text/html"}
                             :methods {:post (fn [ctx] (restricted-content ctx))}
                             ;;Ensure the client is accessing the restricted part only if the token is correct
                             :access-control {:scheme :keycloak
                                              :allow-origin "http://localhost:3449"
                                              :allow-credentials true
                                              :allow-methods #{:get :post :options}
                                              :allow-headers ["Content-Type"
                                                              "Access-Control-Allow-Headers"
                                                              "Authorization"
                                                              "X-Requested-With"
                                                              "X-Authorization-Token"]
                              :authorization {:methods {:get :employee :post :employee}}}})]
    [true (as-resource nil)]]])

(defstate server
  :start (listener routes {:port 8084})
  :stop ((:close server)))

Backend with Ring and Buddy-Auth

Buddy-Auth provides a Ring middleware wrap-authentication that accepts a chain of backends, including token based authentication and authorization backends.

(require '[buddy.auth.backends :as buddy-back :refer [token]]
          [buddy.auth.middleware :as buddy-midd :refer [wrap-authentication]]
          [keycloak.deployment :as kc-deploy :refer [deployment client-conf]]
          [keycloak.backend :as kc-backend :refer [buddy-verify-token-fn]])
          
(def keycloak-deployment (kc-deploy/deployment (kc-deploy/client-conf {:auth-server-url "http://localhost:8090/auth"
                                                                       :admin-realm      "master"
                                                                       :realm            "my-realm"
                                                                       :admin-username   "admin"
                                                                       :admin-password   "adminpass"
                                                                       :client-admin-cli "admin-cli"
                                                                       :client-id        "my-backend"
                                                                       :client-secret    "1d741292-74a0-42c8-99b7-6a6a744ebb25"})))

(def app (-> handler
             (wrap-params)
             (wrap-authentication (buddy-back/token {:authfn (kc-backend/buddy-verify-token-fn keycloak-deployment) :token-name "Bearer"}))))

Backend with Donkey and Buddy-Auth

Donkey is a Ring compliant HTTP server. You can use the same middleware as above, the configuration is just slightly different.

(defn account-data [extracted-token]
  (let [group-path (.get (get-in extracted-token [:other-claims :group]) 0)]
    {:username (:username extracted-token)
     :group (when group-path (subs group-path (inc (last-index-of group-path "/"))))
     :roles (:roles extracted-token)}))

(defn yada-extract-account-data [ctx]
  (when-let [extracted-token (get-in ctx [:authentication "default"])]
    (account-data extracted-token)))

(defn ring-extract-account-data [req]
  (when-let [extracted-token (:identity req)]
    (account-data extracted-token)))


(def routes
   (ring/router [ "/accounts" ["/:account-id" {:handler (fn [req]
                                                              (let [account (ring-extract-account-data req)]))}]]))

(def app (ring/ring-handler routes 
                            (ring/create-default-handler) 
                            {:middleware [[ring.middleware.params/wrap-params]
                                          [wrap-authentication (buddy-back/token {:authfn (kc-backend/buddy-verify-token-fn keycloak-deployment) :token-name "Bearer"})]]}))

(defn start-donkey-server []
  (let [server (-> (donkey/create-donkey)
                   (donkey/create-server {:port 8080
                                          :routes [{:handler app :handler-mode :blocking}]}))]
    (println "Start Backend Donkey Server on port 8080")
    (-> server
        donkey-server/start
        (on-success (fn [_]
                        (println "Backend Donkey server started on port 8080")))
        (on-fail (fn [exception]
                   (println "Failed to start Backend Donkey Server on port 8080")
                   (println (.getMessage exception))
                   (throw exception))))
    server))