[TLS] TLS1.3 Ticket Usage Across Versions

[Steven Collison <[e-mail]>]

Hello,

While testing a TLS1.3 client implementation, I found an unexpected 
behavior. Specific sequence:
1. Client negotiates TLS1.3 with Server.
2. Server sends NST with a valid ticket.
3. Client reconnects to the same Server. The ClientHello contains both 
the `session_ticket` and `pre_shared_key` extensions. The value of the 
`psk_identity` is equal to the value of the `session_ticket`.

Is it ever valid for a client to populate both extensions with the same 
ticket value? Even if the client reconnects and lands on a different 
server node that only supports TLS1.2, resumption should fail because 
the protocol version should be included as part of the session state. 
The `session_ticket`  extension data in this example is at least wasted 
data.

I did not see anything in the spec(neither 8446 2.2 nor 4.6.1) that 
explicitly disallows this. 2.2 contains “Both mechanisms are obsoleted 
in TLS 1.3.” when referring to `session_ticket` and `session_id` 
resumption, but that may not be clear enough.

-Steven