One issue I can see with your param sub is in the foreach loop. You're resetting %out_params each time through that loop instead of adding key/value paris to it. I'm assuming that's not what you want to do.

To add elements, you need to the members of the hash instead of setting the hash equal to a new list:

  foreach my $p (@in_params) {
     $out_params{$p} = $self->{r}->param($p);
  }
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saying %out_params = (...); resets the hash to only the values within the list - (...).

Does this make sense?