I censored the names because the Profile owner is NOT the scammer but seriously the scheme is nearly as old as steam itself If your friend asks you to register on some external website for a tournament or whatever it is, DONT click on the link he is sending you!
This scam is still around because people keep falling for it. If you log in on this side via your steam account you give your steam access away to the scammer, he then will likely sell everything of value on your account and use your account to scam your friends.