It may have 400 years reaffirmed in the Anglican tradition; but the confessional secret has at least 1000 years in Catholic and Orthodox traditions. And there is no indication it was ever in another way before that. The secret is the only choice fitting with the theory behind confession, because you are confessing before God, not before a priest. The priest is not there as a person, but representing God, listening, telling penalties and forgiving in the name of God, not their own.