[SR-Users] SSL errors with websocket clients

[Vinicius Kwiecien Ruoso]

Hi all!
How are you?

I have a kamailio instance and some users are having issues connecting
via websocket using TLS. The logs show SSLv3 errors. Cannot find why
that error would show up if SSLv2/3 is not enabled. Double checked it
via SSLLabs that only TLSv1.2 is allowed in the service.

Error sample:
```
15(36) ERROR: tls [tls_util.h:42]: tls_err_ret(): TLS
accept:error:14094416:SSL routines:ssl3_read_bytes:sslv3 alert
certificate unknown
15(36) ERROR: <core> [core/tcp_read.c:1512]: tcp_read_req(): ERROR:
tcp_read_req: error reading - c: 0x7fafc8768190 r: 0x7fafc8768278 (-1)
```

This instance has close to 400 websocket connections opened during the
day. I have a high log level enabled. I was not able to identify any
reason why this happens. The certificate is a Letsencrypt certificate.

The issue is that sometimes clients have a hard time connecting to the
websocket and that maybe related. Below are a few more details about
the config. Please let me know if you have any pointers on how to
debug those connection issues.

8<-----
TLS config:

modparam("tls", "tls_method", "TLSv1.2+")
modparam("tls", "verify_certificate", 0)
modparam("tls", "require_certificate", 0)
modparam("tls", "low_mem_threshold1", 0)
modparam("tls", "low_mem_threshold2", 0)
modparam("tls", "private_key", "/etc/certs/tls.key")
modparam("tls", "certificate", "/etc/certs/tls.crt")

version: kamailio 5.3.9 (x86_64/linux)
8<-----

This is related to the issue
https://github.com/kamailio/kamailio/issues/3085 (as pointed out it is
not a problem in Kamailio code).

Thanks,
Vinicius