Add CORS headers to HTTP responses

Improve compatibility with other services, by allowing cross origin
requests.

invoice_manager.go

@@ -36,6 +36,7 @@ func (m *InvoiceManager) handleInvoiceCreation(config ServerConfig) http.Handler
 	return func(w http.ResponseWriter, r *http.Request) {
 		log.Infof("Handling invoice creation: %v\n", *r)
 		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("Access-Control-Allow-Origin", "*")
 
 		keys, hasAmount := r.URL.Query()["amount"]
 		if !hasAmount || len(keys[0]) < 1 {

main.go

@@ -151,6 +151,7 @@ func handleLNUrlp(config ServerConfig, metadata string) http.HandlerFunc {
 			Callback:       config.InvoiceCallback,
 		}
 		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("Access-Control-Allow-Origin", "*")
 		w.WriteHeader(http.StatusCreated)
 		json.NewEncoder(w).Encode(resp)
 	}