When connected to an encrypted (WEP/WPA) router, a rogue packet can
cause the ESP8266 WiFi stack to drop to an unecrypted rogue network of
the same SSID.

Handle this by dropping the WiFi connection immediately and reconnecting
to the stored WPA/WEP network requested by the application, whenever the
AUTHMODE changes to OPEN from a secured mode.

https://lbsfilm.at/blog/wpa2-authenticationmode-downgrade-in-espressif-microprocessors
for more details.

The downgrade event needs to be looked for in the main WiFi event
processing function instead of the callback function (which will only
trigger if the user actually makes a callback themselves).