from nx_secure_tls.h:1584
UINT _nx_secure_tls_session_client_callback_set(NX_SECURE_TLS_SESSION *tls_session,
ULONG (*func_ptr)(NX_SECURE_TLS_SESSION *tls_session,
NX_SECURE_TLS_HELLO_EXTENSION *extensions,
UINT num_extensions));
Implemented in nx_secure_tls_session_client_callback_set.c:71