open var sslVersion: String?
Indicates which SSL version or above to use (command are
"default", "tlsv1", "tlsv1.0", "tlsv1.1", "tlsv1.2", "tlsv1.3")
To better control SSL version, we can even use
ssl-version.min = "..." and ssl-version.max = "..."
where "..." is one of the above command. But note these two forms
("setting ssl-version" and "setting both min/max)
can't co-exist.
open fun sslVersion(value: String?): Unit