Session verification

[kloenk]

Currently session verification is not implemented, this is a deal breaker for many users.

[grahamc]

Thanks for filing this ticket, @kloenk! As an administrator for a sizable community it is important for trustworthiness that all my sessions are verified and that I not make a habit of sending messages that are unverified. I'm excited to use Nio!

[genebean]

This, and support for encryption are 100% essential imo. I’m looking forward to seeing them added. Keep up the good work!