FeministWiki membership is not directly open to the public, but every member can add new members at will by using the https://add-member.feministwiki.org/ service.
To detect possible infiltrators, the system keeps track of who was added by who. So if member John Doe turns malicious and starts adding lots of trolls as members who try to wreak havoc within the community, it will be easy to trace them back to John Doe, holding him accountable, and in worst case banning him and every member who was added by him.
While the membership system technically forms a hierarchy (Jane added Sarah, Sarah added Meghan, and so on), the intention is of course not to create "ranks" like there are in a cult. The records of who-added-who are normally invisible to all but the technician, and are only to be looked up in case someone needs to be held accountable for a troll who was granted membership.
Since members can only be added by existing members, this raises the question of who the initial members were. They consist of an array of well-known feminist figureheads (todo: name them), plus the first technician who built the FeministWiki infrastructure.
Since the community is yet in an infantile state, feel free to mail to firstname.lastname@example.org to request membership. You must be able to prove your commitment to the feminist cause.