Bulk DeleteObjects carries the keys in the request body, so the route Auth
middleware ran a single bucket-level check with object="", building the
resource ARN as arn:aws:s3:::<bucket>. That never matches an s3:DeleteObject
policy scoped to <bucket>/*, so the entire batch was denied even though the
single-key DELETE worked with the same credentials.
Defer authorization to the handler and check each key via AuthorizeBatchDeleteKey,
mirroring AuthorizeCopySource: a synthetic DELETE /<bucket>/<key> request resolves
s3:DeleteObject (or s3:DeleteObjectVersion when a versionId is given) against the
object ARN. Denied keys come back as per-key errors while authorized keys still
delete, matching AWS semantics.
