sslh accepts connections on specified ports, and forwards them further based
on tests performed on the first data packet sent by the remote client.

Probes for HTTP, TLS/SSL (including SNI and ALPN), SSH, OpenVPN, tinc, XMPP,
SOCKS5, are implemented, and any other protocol that can be tested using a
regular expression, can be recognised. A typical use case is to allow serving
several services on port 443 (e.g. to connect to SSH from inside a corporate
firewall, which almost never block port 443) while still serving HTTPS on
that port.

Hence sslh acts as a protocol demultiplexer, or a switchboard. With the SNI
and ALPN probe, it makes a good front-end to a virtual host farm hosted
behind a single IP address.

sslh has the bells and whistles expected from a mature daemon: privilege and
capabilities dropping, inetd support, systemd support, transparent proxying,
chroot, logging, IPv4 and IPv6, TCP and UDP, a fork-based and a select-based
model, and more.

WWW: https://www.rutschle.net/tech/sslh.shtml