rs: do not strip authority section in response

[rithvikvibhu]

Fixes buffrr/letsdane#1

Recursive resolvers should return the NSEC record in the AUTHORITY section for successful verification of wildcard records. Trying to do so right now (in both hsd and hnsd) fail with noqname proof not found.

more info: https://datatracker.ietf.org/doc/html/rfc5155#section-8.8

Live example

*.home.htools is a wildcard TLSA record in zone htools at 129.153.177.220.

Start hnsd with:

./hnsd -p 2 -r 127.0.0.1:9592 -n 127.0.0.1:9591 -t -x ~/.hnsd

Without this PR:

❯ delv @127.0.0.1 -p 9592 -a ~/.hsd-ksk _443._tcp.home.htools TLSA +rtrace +vtrace +nosplit
;; fetch: _443._tcp.home.htools/TLSA
;; validating _443._tcp.home.htools/TLSA: starting
;; validating _443._tcp.home.htools/TLSA: attempting positive response validation
;; fetch: htools/DNSKEY
;; validating htools/DNSKEY: starting
;; validating htools/DNSKEY: attempting positive response validation
;; fetch: htools/DS
;; validating htools/DS: starting
;; validating htools/DS: attempting positive response validation
;; fetch: ./DNSKEY
;; validating ./DNSKEY: starting
;; validating ./DNSKEY: attempting positive response validation
;; validating ./DNSKEY: verify rdataset (keyid=35215): success
;; validating ./DNSKEY: marking as secure (DS)
;; validating htools/DS: in fetch_callback_dnskey
;; validating htools/DS: keyset with trust secure
;; validating htools/DS: resuming validate
;; validating htools/DS: verify rdataset (keyid=60944): success
;; validating htools/DS: marking as secure, noqname proof not needed
;; validating htools/DNSKEY: in fetch_callback_ds
;; validating htools/DNSKEY: dsset with trust secure
;; validating htools/DNSKEY: verify rdataset (keyid=24809): success
;; validating htools/DNSKEY: marking as secure (DS)
;; validating _443._tcp.home.htools/TLSA: in fetch_callback_dnskey
;; validating _443._tcp.home.htools/TLSA: keyset with trust secure
;; validating _443._tcp.home.htools/TLSA: resuming validate
;; validating _443._tcp.home.htools/TLSA: verify rdataset (keyid=24809): from wildcard
;; validating _443._tcp.home.htools/TLSA: looking for noqname proof
;; validating _443._tcp.home.htools/TLSA: noqname proof not found
;; no valid NSEC resolving '_443._tcp.home.htools/TLSA/IN': 127.0.0.1#9592
;; resolution failed: no valid NSEC

With this PR:

❯ delv @127.0.0.1 -p 9592 -a ~/.hsd-ksk _443._tcp.home.htools TLSA +rtrace +vtrace +nosplit
;; fetch: _443._tcp.home.htools/TLSA
;; validating _443._tcp.home.htools/TLSA: starting
;; validating _443._tcp.home.htools/TLSA: attempting positive response validation
;; fetch: htools/DNSKEY
;; validating htools/DNSKEY: starting
;; validating htools/DNSKEY: attempting positive response validation
;; fetch: htools/DS
;; validating htools/DS: starting
;; validating htools/DS: attempting positive response validation
;; fetch: ./DNSKEY
;; validating ./DNSKEY: starting
;; validating ./DNSKEY: attempting positive response validation
;; validating ./DNSKEY: verify rdataset (keyid=35215): success
;; validating ./DNSKEY: marking as secure (DS)
;; validating htools/DS: in fetch_callback_dnskey
;; validating htools/DS: keyset with trust secure
;; validating htools/DS: resuming validate
;; validating htools/DS: verify rdataset (keyid=60944): success
;; validating htools/DS: marking as secure, noqname proof not needed
;; validating htools/DNSKEY: in fetch_callback_ds
;; validating htools/DNSKEY: dsset with trust secure
;; validating htools/DNSKEY: verify rdataset (keyid=24809): success
;; validating htools/DNSKEY: marking as secure (DS)
;; validating _443._tcp.home.htools/TLSA: in fetch_callback_dnskey
;; validating _443._tcp.home.htools/TLSA: keyset with trust secure
;; validating _443._tcp.home.htools/TLSA: resuming validate
;; validating _443._tcp.home.htools/TLSA: verify rdataset (keyid=24809): from wildcard
;; validating _443._tcp.home.htools/TLSA: looking for noqname proof
;;   validating _atproto.home.htools/NSEC: starting
;;   validating _atproto.home.htools/NSEC: attempting positive response validation
;;   validating _atproto.home.htools/NSEC: keyset with trust secure
;;   validating _atproto.home.htools/NSEC: verify rdataset (keyid=24809): success
;;   validating _atproto.home.htools/NSEC: marking as secure, noqname proof not needed
;; validating _443._tcp.home.htools/TLSA: in validator_callback_nsec
;; validating _443._tcp.home.htools/TLSA: looking for relevant NSEC
;; validating _443._tcp.home.htools/TLSA: nsec range ok
;; validating _443._tcp.home.htools/TLSA: resuming validate_nx
;; validating _443._tcp.home.htools/TLSA: marking as secure, noqname proof found
; fully validated
_443._tcp.home.htools.  279     IN      TLSA    3 1 1 EFB386BDFB86E2249988443E79123773662CE0F4530BAC08732FFF4E5489262F
_443._tcp.home.htools.  279     IN      RRSIG   TLSA 13 2 3600 20240314000000 20240222000000 24809 htools. +HAPmPsy7X2QSveQMKg7XTZGNyjsQ2OsPFMBwQE0e9tD/PYk5ZXnjvWBY+RTCszzgvh/pdKJNby6r1EXb4PZOg==