This issue is meant to track the progress regarding implementing the key_share extension for DTLS v1.3 (see the parent issue regarding the other tasks for the MVP feature set for DTLS v1.3).

The extension isn't deeply described in RFC 9147 (DTLS v1.3), but it refers to the implementation from section 4.2.8 (including 4.2.8.1 and 4.2.8.2) of RFC 8446 (TLS v1.3).