Make docker image use sratch

cmd/rdpgw/config/configuration.go

@@ -193,6 +193,12 @@ func Load(configFile string) Configuration {
 	if !Conf.Caps.TokenAuth && Conf.Server.Authentication == "openid" {
 		log.Fatalf("openid is configured but tokenauth disabled")
 	}
+
+	// prepend '//' if required for URL parsing
+	if !strings.Contains(Conf.Server.GatewayAddress, "//") {
+		Conf.Server.GatewayAddress = "//" + Conf.Server.GatewayAddress
+	}
+	
 	return Conf
 
 }

cmd/rdpgw/main.go

@@ -88,7 +88,7 @@ func main() {
 			url.Scheme = "https"
 		}
 		url.Path = "callback"
-		api.GatewayAddress = url.Host
+		api.GatewayAddress = url.String()
 
 		oauthConfig := oauth2.Config{
 			ClientID:     conf.OpenId.ClientId,