funciones.go

func enableCORS(router *mux.Router) {
	router.PathPrefix("/").HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
		w.Header().Set("Access-Control-Allow-Origin", "http://localhost")
	}).Methods(http.MethodOptions)
	router.Use(middlewareCors)
}

func middlewareCors(next http.Handler) http.Handler {
	return http.HandlerFunc(
		func(w http.ResponseWriter, req *http.Request) {
			// Just put some headers to allow CORS...
      w.Header().Set("Access-Control-Allow-Origin", "http://localhost")
			w.Header().Set("Access-Control-Allow-Credentials", "true")
			w.Header().Set("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE")
			w.Header().Set("Access-Control-Allow-Headers", "Accept, Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, Authorization")
			// and call next handler!
			next.ServeHTTP(w, req)
		})
}