Store login state in reverse proxy URL

It's easier and less complex than writing a Grav plugin to make backend
requests each time a page is loaded.

skouter.go

@@ -964,7 +964,7 @@ func setTokenCookie(id int, role string, w http.ResponseWriter) error {
 func refreshToken(w http.ResponseWriter, db *sql.DB, r *http.Request) {
 	claims, _ := getClaims(r)
 	
-	if !claims.Valid() {
+	if claims.Valid() != nil {
 		return
 	}
 	
@@ -3571,7 +3571,7 @@ func api(w http.ResponseWriter, r *http.Request) {
 		login(w, db, r)
 	case match(p, "/api/token", &args) &&
 		r.Method == http.MethodGet && guard(r, 1):
-		getToken(w, db, r)
+		refreshToken(w, db, r)
 	case match(p, "/api/letterhead", &args) &&
 		r.Method == http.MethodPost && guard(r, 1):
 		clipLetterhead(w, db, r)
@@ -3717,19 +3717,43 @@ func route(w http.ResponseWriter, r *http.Request) {
 	page.Render(w)
 }
 
+// The grav frontend does not have controllers to communicate state
+// with backend so the user's login status must be represented by a
+// query parameter during proxy.
+func setupProxy(r *httputil.ProxyRequest) {
+	proxyURL, err := url.Parse("http://localhost:8002")
+	if err != nil {
+		log.Fatal("invalid origin server URL")
+	}
+	
+	r.In.ParseForm()
+	claims, _ := getClaims(r.In)
+	q := r.Out.URL.Query()
+	
+	r.SetURL(proxyURL)
+	
+	// Check if user is logged in, then set or delete the logged_in param
+	if claims.Valid() == nil {
+    	q.Set("logged_in", "true")
+	} else {
+		q.Del("logged_in")
+	}
+	
+	r.Out.URL.RawQuery = q.Encode()
+}
+
 func serve() {
 
 	files := http.FileServer(http.Dir(""))
-
-	proxy, err := url.Parse("http://localhost:8002")
-	if err != nil {
-		log.Fatal("invalid origin server URL")
+	
+	proxy := &httputil.ReverseProxy{
+		Rewrite: setupProxy,
 	}
 
 	http.Handle("/assets/", files)
 	http.HandleFunc("/api/", api)
 	http.HandleFunc("/app", route)
-	http.Handle("/", httputil.NewSingleHostReverseProxy(proxy))
+	http.Handle("/", proxy)
 	log.Fatal(http.ListenAndServe(address, nil))
 }