How get the Custom Data of esptouch v2 apk

[Tsingtao]

Hi, I use esptouch v2 apk to config network. I input mqqt data in the Custom Data frame of esptouch v2 apk and press confirm key. At the same time, power on the ESP8266 board, ESP8266 start to smartconfig.
In the sdk, the function of smartconfig_done is the callback of smartconfig. The function of smartconfig_done include SC_STATUS_FIND_CHANNEL, SC_STATUS_GETTING_SSID_PSWD, SC_STATUS_LINK, and SC_STATUS_LINK_OVER. My quesion is how I can get the Custom Data of esptouch v2 apk by function of SDK？
Thanks very much!