Ugly, but seems to work

ampel-firmware/ampel-firmware.ino

@@ -56,6 +56,12 @@
  * and define your credentials and parameters in 'config.h'.
  */
 
+iotwebconf::WifiAuthInfo* failedConnection() {
+  Serial.println("Seriously. What???");
+  led_effects::showKITTWheel(color::red);
+  return nullptr;
+}
+
 /*****************************************************************
  * Setup                                                         *
  *****************************************************************/
@@ -89,10 +95,12 @@ void setup() {
     Serial.println(WiFi.localIP());
   });
 
-  web_config::setWifiConnectionFailedCallback([]() {
-    led_effects::showKITTWheel(color::red);
-    Serial.println(F("Connection to WiFi failed"));
-  });
+  web_config::setWifiFailCallback(failedConnection);
+
+//  web_config::setWifiConnectionFailedCallback([]() {
+//    led_effects::showKITTWheel(color::red);
+//    Serial.println(F("Connection to WiFi failed"));
+//  });
 #endif
 
   pinMode(0, INPUT); // Flash button (used for forced calibration)

ampel-firmware/web_config.cpp

@@ -162,11 +162,8 @@ namespace web_config {
     iotWebConf->setWifiConnectionCallback(function);
   }
 
-  void setWifiConnectionFailedCallback(void (*function)()) {
-    iotWebConf->setWifiConnectionFailedHandler([&function]() -> WifiAuthInfo* {
-      function();
-      return NULL;
-    });
+  void setWifiFailCallback(WifiAuthInfo* (*function)()) {
+    iotWebConf->setWifiConnectionFailedHandler(function);
   }
 
   void initialize() {

ampel-firmware/web_config.h

@@ -2,6 +2,7 @@
 #define AMPEL_WEB_CONFIG_H_
 
 #define STRING_LEN 64
+#include <IotWebConf.h>
 
 #if defined(ESP8266)
 #  include <ESP8266WebServer.h>
@@ -51,7 +52,7 @@ namespace config {
 namespace web_config {
   void initialize();
   void setWifiConnectionCallback(void (*function)());
-  void setWifiConnectionFailedCallback(void (*function)());
+  void setWifiFailCallback(iotwebconf::WifiAuthInfo* (*function)());
   void update();
   //TODO: Add saveConfig(), for e.g. after custom setters. Or simply reset after each configchange?