The quick idea - is 1. Convert all existing passwords in DB to lower case. 2. Add conversion to lower case into signup script, so all new passwords are same. 3. Convert $p var before $db->check_login(...) in check.inc.php Maybe there is cleaner way
No there is no other way, also there will be a problem with .htpasswd plugin and with all integration plugins. So I don't recommend to do this.