[nathanklick]

Fixes #55.

What this changes

The <Directory> block guarding the document root hardcodes Options SymLinksIfOwnerMatch Indexes in all five vhost blocks across the three site templates, and AllowOverride None blocks any .htaccess override, so there is currently no way to turn mod_autoindex off. Combined with HTTPD_SITE_DIRECTORY_INDEX defaulting to disabled when unset, an otherwise unconfigured container answers a directory request with a full listing of its document root — for the gcsfuse use case, the entire object namespace of the mounted bucket.

This adds HTTPD_SITE_DIRECTORY_LISTING_ENABLED and derives the rendered Options list from it:

HTTPD_SITE_DIRECTORY_LISTING_ENABLED	rendered Options
unset (default), or any other value	SymLinksIfOwnerMatch Indexes
0 or false	SymLinksIfOwnerMatch

The templates now substitute ${HTTPD_SITE_DIRECTORY_OPTIONS} the same way they already substitute ${HTTPD_SITE_DIRECTORY_INDEX}. That variable is an implementation detail derived in configure_virtual_hosts and always overwritten there; the boolean is the supported knob.

Why not the existing idioms

• uncomment_config_element (as used for ServerName, OIDCRemoteUserClaim, OIDCXForwardedHeaders) does not fit. Those are directives that are either present or absent. Here the two variants are the same directive with different arguments, so uncommenting would leave two Options lines in one block.
• A second Options -Indexes directive is not viable either. Apache rejects a context that mixes the bare and +/- forms, so it would force the existing directive to be rewritten in +/- form throughout, changing its merge semantics.

Backward compatibility

The toggle is opt-out — only an explicit false or 0 drops Indexes. Leaving the variable unset renders exactly what this image renders today, so the upgrade is a no-op for existing deployments and nothing that relies on listings loses them silently.

HTTPD_SITE_DIRECTORY_OPTIONS also gets a Dockerfile ENV default. An undefined config variable inside an Options directive is a hard parse error (Illegal option ${...}) rather than the warning DirectoryIndex produces for the same situation, so the default keeps the config parsable when Apache is invoked without the entrypoint having run — apache2ctl configtest over docker exec, for instance.

Verification

Against the published 0.4.1 image with these files overlaid, serving a document root containing index.html, somefile.txt and subdir/nested.txt (no index in subdir/):

case	GET /	GET /subdir/	GET /subdir/nested.txt
stock 0.4.1, no overlay	200, listing	200, listing	200
overlay, variable unset	200, listing	200, listing	200
overlay, =0	403	403	200
overlay, =false	403	403	200
overlay, =0 + HTTPD_SITE_DIRECTORY_INDEX=index.html	200, index.html	403	200

Stock and unset-overlay are identical. Disabling the listing suppresses enumeration without affecting retrieval of files by name, and mod_autoindex logs the suppression explicitly (AH01276: ... server-generated directory index forbidden by Options directive).

apache2ctl configtest reports Syntax OK for default-nossl, default-ssl and default-ssl-redirect under both rendered Options values. shellcheck on entrypoint-helper.sh reports nothing beyond the pre-existing SC1091 for the logger.sh source.

Follow-up

Once this ships, applications/apache-httpd-oidc in release-engineering-infrastructure needs a matching httpd.site.directoryListing value and an appVersion bump. The sites it serves (jrs-reports, perf-analytics, cross-ledger-files) all currently run with the chart default directoryIndex: "disabled", which is precisely the combination that produces a browsable listing.