A way that works for me is to pass in a hashref containing my params. That way the order isn't an issue, they're all in one place, and anything optional can be easilly tested for and used/ignored.

sub verify {
  my $params = shift || die("your message");
  ...
}

verify({param1 => $b,
        param2 => "hello",
        param3 => "whatever"});

verify({param1 => $b});
verify({param1 => "hello"});
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It can get pretty hairy though passing in nested data.