The account creation process in the default [[passwordauth]] plugin could
support account moderation by an administrator.  New account signups could

(Random, potentially infeasible idea: save their edits and apply them if
the account gets approved.)

[[passwordauth]] could also support an "account creation password", as a
simplistic anti-spam measure.  (Some wikis edited by a particular group use
an account creation password as an "ask an existing member to get an account"
system.)

[[tag soc]]