If you're using CGI.pm (or any such modules), this may help you...

use CGI qw(:cgi);

# Name of this script, for example
my $script = script_name();

my $query = get_param('action') || 'start';'

my %actions = (
   start        => \&do_start,
   login    => \&do_login
);

&{ $actions{$query} }

sub do_start {
  my $cookie = cookie('cookie_name'),
  # Check $cookie value, note that cookies
  # aren't to be trusted 100%
  if($cookie) {
     showsecretcontent();
  }
  else {
    show_loginpage();
  }
}

sub showsecretcontent {
  # prints secret content page
}

sub show_loginpage {
  # prints login page
  # Have a hidden field and set its name as 'action'
  # and its value to 'login'
}

sub do_login {
  # process results
  do_refresh();
}

sub do_refresh {
  my $cookie = (
    -name    => 'mycookie',
    -value   => 'youareloggedin',
    -path=>'/',
    -expires => '+1y'
  );
  print header (-cookie => $cookie);
  start_html();
  print qq~<META HTTP-EQUIV ="Refresh" CONTENT = "2 ; URL=$script">~;
  print p("You've successfully logged in. Please wait while you're re-
+direced...");
  end_html();
}
[download]

Hope that helps...