Over-the-air-activation OTAA with LMIC

hi mirmit
thanks for your explanation, but did I read correctly between the lines
ttnctl___=__thethingsnetwork-send-v1.ino
APPEUI = // LoRaWAN Application identifier (AppEUI) perfectly clear
DEVEUI = // LoRaWAN DevEUI, unique device ID (LSBF) ok, must be reversed
APPKEY = // LoRaWAN NwkSKey, network session key
??????? = // LoRaWAN AppSKey, application session key <----- still unclear

thanks for spending another minute to clarify