fix #9: right header to force authenticate

More about basic auth: https://developer.mozilla.org/en-US/docs/Web/HTTP/Authentication

auth.go

@@ -13,6 +13,8 @@ import (
 func authMiddleware(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 
+		w.Header().Set("WWW-Authenticate", `Basic realm="Restricted"`)
+
 		auth := strings.SplitN(r.Header.Get("Authorization"), " ", 2)
 
 		if len(auth) != 2 || auth[0] != "Basic" {

main.go

@@ -50,6 +50,7 @@ func main() {
 	handler := http.FileServer(http.Dir(*path))
 
 	if *basicAuth {
+		log.Println("Enabling Basic Auth")
 		if len(*setBasicAuth) != 0 {
 			parseAuth(*setBasicAuth)
 		} else {