implement back-end for update-search-url (defroute in web.lisp).

This feature is for updating the search-url used by this site to call out to the
Meilisearch service (which provides the search database for this website). It
doesn't touch or alter anything on the Meilisearch service/instance/server.

src/web.lisp

@@ -418,6 +418,27 @@
 			    "error")
 	   (redirect "/login"))))))
 
+(defroute ("/site-settings/update-search-url" :method :POST) ()
+  (destructuring-bind
+      (&key search-url authenticity-token &allow-other-keys)
+      (utils:request-params (lack.request:request-body-parameters ningle:*request*))
+    (if (not (string= authenticity-token (auth:csrf-token)))
+	`(,+forbidden+ (:content-type "text/plain") ("Denied"))
+	(hermetic:auth
+	 (:administrator)
+	 ;; Authorised
+	 (cond ((validation:string-is-nil-or-empty? search-url)
+		(utils:set-alert "No Search URL provided." "missing-data")
+		(redirect "/site-settings"))
+	       (t (nera:update-search-url search-url)
+		  (utils:set-alert "Search URL updated." "success")
+		  (redirect "/site-settings")))
+	 ;; Not Authorised
+	 (progn
+	   (utils:set-alert "You are not authorised to view this page."
+			    "error")
+	   (redirect "/login"))))))
+
 (defroute ("/users" :method :GET) ()
   (hermetic:auth (:administrator)
 		 ;; Authorised