Which solver do you need in order to issue a wildcard certificate?

Why this is the answer

Wildcards are issued through DNS01: the proof lives in the zone, which is the only place that can speak for every name the wildcard covers. HTTP01 cannot work because there is no single host to fetch a key from — a wildcard stands for arbitrarily many. The solver very much does matter here, which is why clusters often configure DNS01 alongside HTTP01. And no ACME flow requires two challenge types at once.