fix: Auto-sense server DTLS 1.2 fallback honors PSK mode#103
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An auto-sense server falling back from DTLS 1.3 to DTLS 1.2 unconditionally constructed a certificate-auth Server12, so a server built with `Dtls::new_auto` and `with_psk_server(...)` rejected DTLS 1.2 PSK clients with "No mutually acceptable cipher suite". Peek at the buffered ClientHello to mirror the suite Server12 would pick and construct the matching auth mode before replay. Fixes #100
xnorpx
approved these changes
Apr 23, 2026
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Summary
Dtls::new_autoalways built a certificate-authServer12on DTLS 1.3 to 1.2 fallback, so a PSK server config could not accept DTLS 1.2 PSK clients.Server12::new_pskorServer12::newto match. Fragmented first-fragments (fragment_offset > 0) are skipped and the next buffered packet is tried.Fixes #100
Test plan
auto_server_psk_fallback_with_dtls12_psk_clientfails onmainand passes with the fix.cargo test --features rcgen(401 tests pass).cargo clippy --features rcgenclean for the library.