#!/usr/bin/perl -T

use strict;
use warnings;

if ( ... a password was not provided ... ) {
   ... return HTML login form form ...
   exit;
}

if ( ... password is not ok ... ) {
   ... return HTTP error + HTML error message and login form ...
   exit;
}

$file_name = ...;

if ( ... insufficient permissions... ) {
   ... return HTTP error + HTML error message ...
   exit;
}

if (!open(my $fh, '<', $file_name)) {
   ... return HTTP error and/or HTML error message ...
   exit;
}
 
print("Content-Type: application/octect-stream\n");
print("\n");

binmode(STDOUT);
binmode($fh);
$/ = \1024; # Read in blocks of 1024 bytes;
print while <$fh>;