Allow CORS to GitHub raw

Signed-off-by: Alex Ellis <alexellis2@gmail.com>

gateway/handlers/cors.go

@@ -0,0 +1,24 @@
+package handlers
+
+import "net/http"
+
+type CorsHandler struct {
+	Upstream    *http.Handler
+	AllowedHost string
+}
+
+func (c CorsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// https://raw.githubusercontent.com/openfaas/store/master/store.json
+	w.Header().Set("Access-Control-Allow-Headers", "Content-Type")
+	w.Header().Set("Access-Control-Allow-Methods", "GET")
+	w.Header().Set("Access-Control-Allow-Origin", c.AllowedHost)
+
+	(*c.Upstream).ServeHTTP(w, r)
+}
+
+func DecorateWithCORS(upstream http.Handler, allowedHost string) http.Handler {
+	return CorsHandler{
+		Upstream:    &upstream,
+		AllowedHost: allowedHost,
+	}
+}