Add the second header.

my $cookie1 = CGI::cookie( "-name" => "foo", "-value" => "a" );
my $cookie2 = CGI::cookie( "-name" => "bar", "-value" => "3" );
$r->headers_out->{"Set-Cookie"} = $cookie1;
$r->headers_out->add("Set-Cookie" => $cookie2);
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