The convention is that the secretary to the cabinet has the authority to waive cabinet confidences. There's jurisprudence on this. As was clear from the SNC-Lavalin case, the Prime Minister himself, of course, can opt to waive cabinet confidence, but traditionally that duty falls to the clerk and there is jurisprudence on the criteria that the clerk has to follow on this.
On July 21st, 2020. See this statement in context.