use Digest::MD5 qw(md5_hex)

my %passwd = (
  joe => ["I'maSalt", md5_hex("I'maSalt - secret")],
);

sub login {
    my ($user, $pass) = @_;
    if( my $pa = $passwd{$user} ) {
        return 1 if md5_hex("$pa->[0] - $pass") eq $pa->[1];
    }
    return 0;
}