Clojure in the Service of Her Majesty's Government

GOV.UK Verify benefits

single set of credentials for all of government
services don't have to reinvent the wheel
separation of data:
- services don't get access unless you log in to them
- identity providers don't know which service you're using

Technical questions

What would the architecture look like?

How many components are there?

How are responsibilities split?

http requests and responses are maps

(defn app-routes [config]
  (handler/site
    (routes
      (GET "/hello/:name" [name :as request]
        (fail-> request
               (re/validate! :headers-contain "mock_authorization")
               (resp/get-header "mock_authorization")
               (say-hello name config))))))

(defonce candela nil)

(defn go []
  (alter-var-root #'candela
    (constantly (jetty/run-jetty (cweb/app config)))))

(defn stop []
  (.stop candela))

(defn reset []
  (stop)
  (repl/refresh :after 'user/go))

so you define a reset function in user.clj this is loaded by default when you start the repl stops the running app reloads changed namespaces creates and starts the app again all within the same jvm so super fast the other great thing about this, that you can’t really see from this example - is that we actually ended up with about 5 different web services that we were running at once. The reloaded workflow meant that we could make a change to a bit of code that was used by more than one of the services, and by calling refresh, both would pick up the changes straightaway. definitely recommend getting this working as soon as possible, we left it quite late the only thing that was not so awesome with this, and we’ll talk more about this later is when we wanted to change something on the ui we used enlive for templating, and had jade files that produced html when a jade or html file changed on disk it was not picked up by the reloaded flow this was the only limitation we found

(-> (session ring-app)
  (visit "/")
  (follow "login")
  (fill-in "User:" "username")
  (fill-in "Password:" "password")
  (press "Login")
  (follow-redirect)
  (has (missing? [:#no-such-element])
       "User shouldn't see the no-such-element"))

(-> (ida-session (combined-handler)
  (visit "http://wands.gov.uk/register")
  (helpers/sign-in)
  (follow "Delegate your authority")
  (visit "http://wands.gov.uk/persist-delegation"
         :request-method :post)
  (follow-redirect) ; to Identity Provider
  (press "Continue")
  (follow-redirect) ; back to service
  (check-response
    (should-redirect-to
      "http://wands.gov.uk/"))))

(defn combined-handler []
  (let [apps {"idp.com"       michie/handler
              "orch.gov.uk"   knox/handler
              "wands.gov.uk"  candela/handler
              "orgs.gov.uk"   al-kindi/handler
              "agents.gov.uk" wheatstone/handler}]
    (fn [req]
      (let [app (get apps (:server-name req)
                     default-handler)]
        (app req)))))

would we use clojure for a similar project?

Links

GOV.UK Verify identityassurance.blog.gov.uk
- identity assurance for organisations and agents
Government Service Design Manual www.gov.uk/service-manual
- especially Alpha phase
- and ending the alpha
Jay Fields: REPL-driven development
Giles Alexander: Hitch-hiking anti-pattern
Stuart Sierra: My Clojure Workflow, Reloaded
Emacs Cheatsheet www.rgrjr.com/emacs/emacs_cheat.html
Clojure Cheatsheet clojure.org/cheatsheet