cert_ext_add
cert_ext_add("force-command", certflags_command, 1);
cert_ext_add("source-address", certflags_src_addr, 1);
cert_ext_add("verify-required", NULL, 1);
cert_ext_add("permit-X11-forwarding", NULL, 0);
cert_ext_add("permit-agent-forwarding", NULL, 0);
cert_ext_add("permit-port-forwarding", NULL, 0);
cert_ext_add("permit-pty", NULL, 0);
cert_ext_add("permit-user-rc", NULL, 0);
cert_ext_add("no-touch-required", NULL, 0);
cert_ext_add(val, cp, iscrit);