constraints => {
    ipf_password => {
       constraint => \&check_password,
       params     => [ qw( ipf_password ipf_confirm_password ) ],
    },
}

##</code><code>##

constraints => {
    ipf_password => {
       constraint => sub { $_[0] eq $_[1] },
       params     => [ qw( ipf_password ipf_confirm_password ) ],
    },
}