Setting a bad S3 endpoint can delete filestore if eventual/_add symlink is set

If you set an S3 endpoint in your storage.properties file and that endpoint goes to a page that returns 200 (like standard HTML like a login page) then Artifactory will see the 200 when checking if a file exists on the bucket, take that as confirmed file exists, skip uploading and delete it from the filestore. This has the effect of deleting the whole filestore. If no backup was made this could cause a serious situation.

We need to check that the endpoint is valid before performing any filesync or some other logical way to prevent this.