Server and command line tools now support option --tls_version to specify the
TLS version between client and server. Valid values are TLSv1.0, TLSv1.1, TLSv1.2, TLSv1.3
or a combination of them. E.g.

--tls_version=TLSv1.3
--tls_version=TLSv1.2,TLSv1.3

In case there is a gap between versions, the lowest version will be used:
--tls_version=TLSv1.1,TLSv1.3 -> Only TLSv1.1 will be available.

If the used TLS library doesn't support the specified TLS version, it will use
the default configuration.

Limitations:

SSLv3 is not supported. The default configuration doesn't support TLSv1.0 anymore.
TLSv1.3 protocol currently is only supported by OpenSSL 1.1.0 (client and server) and
GnuTLS 3.6.5 (client only).

Overview of TLS implementations and protocols

Server:

+-----------+-----------------------------------------+
| Library   | Supported TLS versions                  |
+-----------+-----------------------------------------+
| WolfSSL   | TLSv1.1, TLSv1,2                        |
+-----------+-----------------------------------------+
| OpenSSL   | (TLSv1.0), TLSv1.1, TLSv1,2, TLSv1.3    |
+-----------+-----------------------------------------+
| LibreSSL  | (TLSv1.0), TLSv1.1, TLSv1,2, TLSv1.3    |
+-----------+-----------------------------------------+

Client (MariaDB Connector/C)
+-----------+-----------------------------------------+
| Library   | Supported TLS versions                  |
+-----------+-----------------------------------------+
| GnuTLS    | (TLSv1.0), TLSv1.1, TLSv1.2, TLSv1.3    |
+-----------+-----------------------------------------+
| Schannel  | (TLSv1.0), TLSv1.1, TLSv1.2             |
+-----------+-----------------------------------------+
| OpenSSL   | (TLSv1.0), TLSv1.1, TLSv1,2, TLSv1.3    |
+-----------+-----------------------------------------+
| LibreSSL  | (TLSv1.0), TLSv1.1, TLSv1,2, TLSv1.3    |
+-----------+-----------------------------------------+