Backspace ^H vs ^?. How to know

[ArthurSonzogni]

I am trying to solve: https://github.com/ArthurSonzogni/FTXUI/issues/4

1. When I start kmscon, I end up in the login area. I observe the backspace is replaced by ^H.
2. Then (after login), backspace are interpreted as "erase on character on the left and move the cursor to the left". Great!
3. Then I start some custom C++ code. When Backspace is pressed, it receives 8 ( =^H) instead of 127 (=^?). I tried to use termios, when I access termios::c_cc[VERASE], it returns 127. I expected to get 8, since it is what kmscon is sending.

I am mostly interested in solving 3) Do you have any idea what my C++ program can do to know what kmscon will be sending?