Only needed for rest-server repos that distinguish an append-only - user (everyday backups) from a delete-capable user (prune / - forget). For S3 / B2 / SFTP / local, leave this blank — the - everyday repo credentials handle prune too. + user (everyday backups) from a delete-capable user (prune). Note + that forget always runs with the everyday repo + credentials, so those must have delete authority. For S3 / B2 / + SFTP / local, leave this blank — but note that prune is + skipped entirely when this is unset, on any backend.