Access blob metadata in two steps: get SAS URL then HTTP request: HEAD to read or PUT to write.
Accessing blob tags is not that easy but get your SAS key that allows tag manipulation elsewhere then come back and finish the job.
Tip #1376: Antivirus for portal attachments
One taketh one giveth (or other way around). Returning a favor to AK who asked: How does the portals handle uploading of virus? (Want your favor returned? Send your awesome tip to jar@crmtipoftheday.com!) There are multiple mechanisms you can put in place to protect your users from the viruses (no, not that virus, unfortunately).