But in the same time Login's wiki states:
A login or logon (also called logging in or on and signing in or on) is the process by which individual access to a computer system is controlled by identification of the user using credentials provided by the user.
From my point of view login is authentication, one of the sub-processes during authentication, a part of it. Authentication is more global and general term, so separate tags existence makes no sense for me, and I vote for synonymizing. Don't you?