13.5 Post-handshake messages
In TLS 1.3, Alice and Bob can send further messages after their main handshake. These post-handshake messages have the handshake content type and are encrypted under the corresponding application traffic key.
13.5.1 The NewSessionTicket message
Any time after receiving Bob’s Finished message, Alice can send a NewSessionTicket message. NewSessionTicket creates a unique link between the value of the ticket and the secret pre-shared key that is derived from resumption˙master˙secret (see Section 12.2, TLS secrets, in Chapter 12, Secrets and Keys in TLS 1.3, for more details).
Bob, in turn, can use this pre-shared key for future handshakes with Alice by including that ticket value in the pre˙shared˙key extension in his ClientHello message.
Alice can also send Bob multiple tickets. As an example, she could send a new ticket following the post-handshake authentication so she can encapsulate the additional client authentication...
