[Tls-reg-review] TLS ALPN registry: Request to add CoAP-over-UDP

[Christian Amsüss <[e-mail]>]

Dear TLS experts,

please have the following entry added into the TLS ALPN registry:

* Protocol: CoAP-over-DTLS
* Identification sequence: 0x63 0x6f ("co")
* Reference: RFC7252

RFC7252 did not register this because it predates ALPNs (it does
describe CoAP and its use of DTLS), but there are now use cases related
to dns-over-coap [1] and SVCB. This registration does not (can not, and
does not intend to) change whether CoAP clients should send an ALPN, but
later documents could change that (eg. [2] that concerns itself with
DTLS1.3 used with CoAP).

Given that the underlying protocol is used in constrained environments
that are sensitive to message sizes, the short identifier should be
warranted.

Note that there is already an entry for "coap", but that refers to
CoAP-over-TLS.  If possible, please consider updating the "CoAP" (0x63
0x6f 0x61 0x70) entry to say "CoAP-over-TLS" to avoid confusion. This
is following the recommendation at [5] to not attempt reusing the same
ALPN for both the DTLS and the TLS version of a protocol.

This is an individual request, which AIU should suffice for this
registry given there is a document out already. I did check briefly with
the CoRE group, and while not being a consensus question, got positive
feedback from there[3][4].

Best regards
Christian

[1]: https://datatracker.ietf.org/doc/draft-ietf-core-dns-over-coap/
[2]: https://datatracker.ietf.org/doc/draft-ietf-anima-constrained-voucher/
[3]: https://mailarchive.ietf.org/arch/browse/core/?gbt=1&index=3Ih6grC8j0JxPuOQqdaFFjSC0r4
[4]: https://datatracker.ietf.org/doc/minutes-interim-2024-core-04-202402281500/#request-for-an-alpn-for-coap-over-dtls-5min-ca

-- 
This may seem a bit weird, but that's okay, because it is weird.
  -- perldata(1) about perl variables