XF 2.2 How can I get xf_session?

[Jenenj]

Hello! I am doing an application in c++. I use Xenforo api as an auth. For the first login, I use /api/auth/. Yes, it is work! . For the after login, I wanna use /api/auth/from-session. I try to get xf_session in the first "api/auth/", but the cookie is empty. So, How can I the xf_session in c++? Thanks !