When publishing content to ArcGIS Enterprise users have the ability to provide metadata at both ArcGIS Server Service level, and ArcGIS Enterprise Portal content item level.
Within ArcGIS Enterprise Portal the Metadata can be accessed via the “Metadata” button on the right-hand side of the item details page
Service level metadata can also be found on the same page, but it is accessed through a “Metadata” link recorded against the Feature Layer.
Content item metadata opens within the ArcGIS Enterprise Portal sharing directory
Service metadata opens within the ArcGIS Server REST directory.
These two pages look largely the same when ArcGIS Server REST, and ArcGIS Enterprise Sharing, directories are enabled.
Through help pages for portalscan and serverscan Esri encourage users to disable these directories. Whilst disabled the ArcGIS Enterprise sharing directory leaves the content item metadata page available, disabling the ArcGIS REST directory also disabled the default metadata page offered to users from the content item details page.
As such, when a user browses to the service level metadata they are presented with a 403 response.
It would be beneficial if the ArcGIS Server REST directory metadata pages presented to via the content item details page continued to work when ArcGIS Server REST directory browsing was disabled.
The ArcGIS Server help suggests that a different /info/metadata should be used when attempting to access Service metadata. This loads a page largely similar to the disabled REST service directory page, which is accessible even when directory browsing is disabled.
Alternatively manipulating the default metadata url provided from the portal content item details page, changing &f=html to &f=xml , will also result in metadata being presented.