Change-Id: I93e73f16474b4b31f7097af2f9479822dfc34c5c
Reviewed-on: https://go-review.googlesource.com/20678
Reviewed-by: Adam Langley <agl@golang.org>

This change adds a new method to tls.Config, SetSessionTicketKeys, that
changes the key used to encrypt session tickets while the server is
running. Additional keys may be provided that will be used to maintain
continuity while rotating keys. If a ticket encrypted with an old key is
provided by the client, the server will resume the session and provide
the client with a ticket encrypted using the new key.

Fixes #9994

Change-Id: Idbc16b10ff39616109a51ed39a6fa208faad5b4e
Reviewed-on: https://go-review.googlesource.com/9072
Reviewed-by: Jonathan Rudenberg <jonathan@titanous.com>
Reviewed-by: Adam Langley <agl@golang.org>

LGTM=r
R=r, adg, rsc
https://golang.org/cl/148080043

Session resumption saves a round trip and removes the need to perform
the public-key operations of a TLS handshake when both the client and
server support it (which is true of Firefox and Chrome, at least).

R=golang-dev, bradfitz, rsc
CC=golang-dev
https://golang.org/cl/6555051