Previously, when dnssec-cds copied CDS records to make DS records,
its -a algorithm option did not have any effect. This means that if
the child zone is signed with older software that generates SHA-1 CDS
records, dnssec-cds would (by default) create SHA-1 DS records in
violation of RFC 8624.
This change makes the dnssec-cds -a option apply to CDS records as
well as CDNSKEY records. In the CDS case, the -a algorithms are the
acceptable subset of possible CDS algorithms. If none of the CDS
records are acceptable, dnssec-cds tries to generate DS records from
CDNSKEY records.
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