I think that your problem is: 
print $q->header( -cookie => [ $set_session, $set_username ] ,  $q->re
+direct("http://localhost/"));

[download]
This works for me: 
#!/usr/bin/perl 

use strict;
use warnings;
use CGI;

my $user_name = 'user';
my $secret = 'password';

my $q = CGI->new;

my $set_username = $q->cookie(
    -name => "user_name",
    -value => $user_name,
    -expires => "+1d",
);

my $set_session = $q->cookie(
    -name => "session",
    -value => $secret,
    -expires => "+1d",
);
print $q->header( -cookie => [ $set_session, $set_username ]);
print $q->redirect('http://localhost/');

[download]

In reply to Re: CGI error: "Invalid header value contains a newline not followed by whitespace" by Khen1950fx
in thread CGI error: "Invalid header value contains a newline not followed by whitespace" by MyMonkName

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