* s3tables: resolve account-less identities to a distinct principal
Static identities with no account block default to the shared admin
account, so getAccountID returned "admin" for every such user and the
permission checks treated them all as the admin principal. Only keep the
admin account when the identity actually carries an admin action;
otherwise fall back to the unique identity name.
* s3tables: limit the open-by-default fallback to anonymous access
The legacy permission path allowed any request that no policy explicitly
denied whenever default-allow was on, which is the zero-config default.
That let an authenticated identity without table permissions reach table
resources owned by others. Restrict the fallback to requests with no
identity or the anonymous identity; authenticated callers must pass an
explicit action or policy check. Zero-config and anonymous access are
unchanged.
* s3tables: drop the no-op ListTableBuckets account gate
The top-level check passed the principal as its own owner, so it always
allowed. Per-bucket filtering in the loop is the real authority; remove
the dead gate and the now-unused locals.
* s3tables: derive the Iceberg catalog's default-allow from auth state
The Iceberg catalog reuses the S3 Tables Manager, which hardcoded
default-allow on. Authenticated callers were enforced only because the
identity struct happens to propagate into the handler; if it were ever
dropped, a secured catalog would fall open. Mirror the S3 port and set
the Manager's default-allow from the authenticator, so an authenticated
caller is enforced regardless. Shell and admin keep their own trusted
Manager. Regression test covers the struct, name-only, and admin paths.
* s3tables: drop redundant ACTION_ADMIN string conversion
ACTION_ADMIN is an untyped string constant, so the conversion is a no-op.
* s3tables: enforce name-only authenticated callers, add trusted bypass
defaultAllowFor treated a request with no identity object as anonymous,
but the Manager path forwards only the identity name (not the struct).
A name-only authenticated caller could therefore be misclassified as
anonymous and allowed under the open default. Treat a server-set identity
name as authenticated too, and add an explicit trusted flag for the local
shell/admin tooling that legitimately bypasses authorization.
* s3tables: trim verbose comments
Chris Lu
b13463880c