- Returns: {string|null}
Returns a string containing the negotiated SSL/TLS protocol version of the
current connection. The value 'unknown'
will be returned for connected
sockets that have not completed the handshaking process. The value null
will
be returned for server sockets or disconnected client sockets.
Protocol versions are:
'SSLv3'
'TLSv1'
'TLSv1.1'
'TLSv1.2'
'TLSv1.3'
See the OpenSSL [SSL_get_version
][] documentation for more information.