SSL_callback_ctrl
long SSL_callback_ctrl(SSL *, int, void (*)(void));
SSL_callback_ctrl(ssl, SSL_CTRL_SET_TLSEXT_DEBUG_CB, \
SSL_callback_ctrl(ssl, SSL_CTRL_SET_MSG_CALLBACK, (void (*)(void))cb);
SSL_callback_ctrl(ssl, SSL_CTRL_SET_NOT_RESUMABLE_SESS_CB,
SSL_callback_ctrl(ssl, SSL_CTRL_SET_TMP_DH_CB, (void (*)(void))dh);