ocserv crashed when use certificate authentication with session-control

[George Panda]

Hello, I am using ocserv 0.8.6 with GnuTLS 3.2.18.

Let's say we use certificate as the only auth method, with
session-control = true (which is enabled by default in
doc/sample.config file).
The ocserv will crash when client trying to connect.

Here is the log, I have removed unnecessary entries.

ocserv[32190]: sec-mod: cmd [size=43] sm: auth init
ocserv[32190]: sec-mod: auth init for user 'user' (group: 'admins')
from '135.35.236.173'
ocserv[32200]: worker: 135.35.236.173:41714 received auth reply
message (value: 1)
ocserv[32200]: worker: 135.35.236.173:41714 user 'user' obtained cookie
ocserv[32189]: main: 135.35.236.173:41714 main-misc.c:423: command socket closed
ocserv[32189]: main: 135.35.236.173:41714 removing client '' with id '32200'
ocserv[32189]: main: main.c:492: ocserv-secmod died unexpectedly

Sec-mod crashed at line "module->open_session == NULL" in function
"handle_sec_auth_res", file "src/sec-mod-auth.c".
I think the reason should be when "sec_auth_init" is called, but
"config->auth_types" is "certificate", which make module not
initialized.

It would be better if we give an friendly error message for this
situation when ocserv is starting.
Thanks.

Best regards
George.P