Don't do that. You're hardcoding the subclass's name in the superclass, so now you can only handle 1 subclass. Also, superclasses should NOT know about subclasses. One obvious solution to this problem is to use a seperate factory object to create instances. Doing it this way will also make sure you only pass the relevant attributes to the class constructor.

package ClassFactory;

sub new {
  my ($class,%auth_vars) = @_;
  return bless \%auth_vars,$class;
}

sub create {
  my ($self,$class) = @_;
  return $class->new(%$self);
}
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Which you can then use as follows:

my $factory = Class::Factory->new( auth vars );

my $obj = $factory->create("Class");
my $subobj = $factory->create("Class::SubClass");
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