bug: auto-sense server fallback to DTLS 1.2 ignores PSK mode

[HMBSbige]

An auto-sense server falling back from DTLS 1.3 to DTLS 1.2 unconditionally constructs the certificate-auth Server12, so a server built with Dtls::new_auto and a with_psk_server(...) config cannot accept a DTLS 1.2 PSK client — the handshake fails with No mutually acceptable cipher suite. The same PSK config works via Dtls::new_12_psk.

dimpl/src/lib.rs

Lines 520 to 540 in cda235a

	fn handle_pending_auto_server(&mut self) -> Result<(), Error> {
	// Take buffered packets and last_now from the Server13 before replacing it.
	// unwrap: is ok, because we can only be here if the inner is a Server13.
	let server = match self.inner.take().unwrap() {
	Inner::Server13(server) => server,
	_ => unreachable!(),
	};
	let (config, cert, now, buffered) = server.into_parts();
	let mut server12 = Server12::new(config, cert, now);
	server12.handle_timeout(now)?;
	self.inner = Some(Inner::Server12(server12));
	for p in &buffered {
	self.handle_packet(p)?;
	}
	Ok(())
	}

[algesten]

@HMBSbige thanks!

Do you think I should avoid cutting a 0.6.0 release?

[HMBSbige]

Yeah, I'd hold off on 0.6.0 and fold the fix in first.

[algesten]

@HMBSbige ok! let's wait!