Support STARTTLS

[clue]

Originally reported 2016-10-04 by @arnaud-lb: reactphp-legacy/socket-client#69

[ellisonpatterson]

Any possibility this will ever be supported?

[clue]

@ellisonpatterson Definitely on the roadmap and would love to see this feature! 👍

That said, there are currently no immediate plans to build this from my end (no demand at the moment and more important outstanding issues currently), but we always welcome PRs! If you need this for a commercial project and you want to help sponsor this feature, feel free to reach out and I'm happy to take a look.

[WyriHaximus]

@clue @ellisonpatterson Spent the better part of this today looking into voryx/PgAsync#38 and it looks like STARTTLS, or put better, the ability to enable TLS encryption on a connection at some point after the connection has been opened and used is required there as well. Had a look at #199 and it looks overly complex for what we need.

In short, we need the tls connection context and the ability to enable the TLS when both sides negotiate to be ready for it. Most of what is required for this is already in this package. I'll look into how this can be achieved without breaking out current API, if a break is required this could land in v3.