crypto/tls: improved 0-RTT QUIC API

Add synchronous management of stored sessions to QUICConn.

This adds QUICStoreSession and QUICResumeSession events,
permitting a QUIC implementation to handle session resumption
as part of its regular event loop processing.

Fixes #63691

Change-Id: I9fe16207cc1986eac084869675bc36e227cbf3f0
Reviewed-on: https://go-review.googlesource.com/c/go/+/536935
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Marten Seemann <martenseemann@gmail.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>

ticket.go

@@ -96,6 +96,7 @@ type SessionState struct {
 	// Client-side TLS 1.3-only fields.
 	useBy  uint64 // seconds since UNIX epoch
 	ageAdd uint32
+	ticket []byte
 }
 
 // Bytes encodes the session, including any private fields, so that it can be
@@ -396,7 +397,6 @@ func (c *Config) decryptTicket(encrypted []byte, ticketKeys []ticketKey) []byte
 // ClientSessionState contains the state needed by a client to
 // resume a previous TLS session.
 type ClientSessionState struct {
-	ticket  []byte
 	session *SessionState
 }
 
@@ -406,7 +406,10 @@ type ClientSessionState struct {
 // It can be called by [ClientSessionCache.Put] to serialize (with
 // [SessionState.Bytes]) and store the session.
 func (cs *ClientSessionState) ResumptionState() (ticket []byte, state *SessionState, err error) {
-	return cs.ticket, cs.session, nil
+	if cs == nil || cs.session == nil {
+		return nil, nil, nil
+	}
+	return cs.session.ticket, cs.session, nil
 }
 
 // NewResumptionState returns a state value that can be returned by
@@ -415,7 +418,8 @@ func (cs *ClientSessionState) ResumptionState() (ticket []byte, state *SessionSt
 // state needs to be returned by [ParseSessionState], and the ticket and session
 // state must have been returned by [ClientSessionState.ResumptionState].
 func NewResumptionState(ticket []byte, state *SessionState) (*ClientSessionState, error) {
+	state.ticket = ticket
 	return &ClientSessionState{
-		ticket: ticket, session: state,
+		session: state,
 	}, nil
 }