'genPattern' => [ 'type' => 'string', 'default' => '*Unregistered $1' ],
'matchPattern' => [ 'type' => 'string|array', 'default' => '*$1' ],
'reservedPattern' => [ 'type' => 'string|null', 'default' => null ],

- genPattern: (string) The pattern used when generating new usernames.
  This should have "$1" indicating the place where the serial string will
  be substituted.
- matchPattern: (string|string[]) The pattern used when determining whether a
  username is a temporary user. This affects the rights of the user
  and also prevents explicit creation of users with matching names.
  This is ignored if "enabled" is false.
- reservedPattern: (string) A pattern used to determine whether a
  username should be denied for explicit creation, in addition to
  matchPattern. This is used even if "enabled" is false.

$wgAutoCreateTempUser['genPattern'] = '~$1';
$wgAutoCreateTempUser['matchPattern'] = ['*$1', '~2$1'];
$wgAutoCreateTempUser['reservedPattern'] = '~$1';
$wgAutoCreateTempUser['serialProvider']['useYear'] = true;