In TLS 1.2 and below, this functionality was provided by "session IDs" and "session tickets" [RFC5077]. Both mechanisms are obsoleted in TLS 1.3.
你的确发现了协议中的一个不够明确的规定，关于 PSK 的东西可以先不管着，那个很容易搞。
IMPORTANT NOTE: The security properties for 0-RTT data are weaker than those for other kinds of TLS data. Specifically:
1. This data is not forward secret, as it is encrypted solely under keys derived using the offered PSK.
2. There are no guarantees of non-replay between connections. Protection against replay for ordinary TLS 1.3 1-RTT data is provided via the server's Random value, but 0-RTT data does not depend on the ServerHello and therefore has weaker guarantees. This is especially relevant if the data is authenticated either with TLS client authentication or inside the application protocol. The same warnings apply to any use of the early_exporter_master_secret.