signature
void gnutls_sign_algorithm_set_server (gnutls_session_t session, gnutls_sign_algorithm_t sign);
gnutls_session_t session
gnutls_sign_algorithm_t sign
void gnutls_sign_algorithm_set_client (gnutls_session_t session, gnutls_sign_algorithm_t sign);
extern const hello_ext_entry_st ext_mod_sig;