password protected registration

Hi guys is there some extension which makes a passwrd protected registration field in registration form ? I mean before user can send registration - user have to type correct password to appropriate field...

I suppose you can add a new join field item and have it marked as mandatory, with it set to only accept one entry, which would mean that if the user typed in the wrong "password," the join request would be denied. Alternatively, you can set the ability to join your web site to only those who have received an invitation, which can be configured from administration, settings, advanced settings. You can also password-protect access to the join.php file through the authorization abilities of Apache.

Thax for directing me right way :-) ... But if I make new field called password , make it mandatory  but how I set this field to be compared to value I want ?