We protect our wiki sites from abuse by establishing a single author for each one. The first author to login to a site will in effect claim that site. There won't be a second login allowed.
A site that has not yet been claimed will suggest that you "Claim with your Email". You must create a Mozilla Persona account, login to that account, and then use that account to claim your wiki.
Earlier versions of wiki used OpenID to claim sites. OpenID providers are vanishing fast. Both OpenID and Persona store some login info in the .wiki/state folder. Erase this information to unclaim a site.