To me, a link to an authoritative source would be a link to the web page (or pdf file) on the site of the journal that published the paper.
You wouldn't link to your friend's mailbox if it was your friend who sent you a copy of the article; why would you link to scihub for basically the same?
You wouldn't link to your friend's mailbox if it was your friend who sent you a copy of the article; why would you link to scihub for basically the same?