Add support for IRCv3 Strict Transport Security (CAP sts)
The IRCv3 Working Group has released a specification for Strict Transport Security (STS): a mechanism allowing servers to advertise a policy that clients may only connect to them over secure connections. It's pretty much the IRC equivalent of an HTTP to HTTPS redirect together with HSTS.
The specification can be found at:
I'm sure that many people would want to see this in Quassel eventually, as in this day and age, there's arguably little to no use for plaintext connections. Deploying this would be a vital step in getting more users to move from plaintext to secure connections.
A few IRCd's have begun adding sts support (see: https://ircv3.net/software/servers.html), so the intent from the server side is present. On the client side, only IRC Cloud has added sts support to date, but I foresee clients such as issi/mIRC/etc. getting involved before too long.