my %env_to_httpheader = (
        'HTTP_USER_AGENT'       => 'User-Agent',
        'HTTP_HOST'             => 'Host',
        'HTTP_TE'               => 'Accept-Encoding',
        'CONTENT_LENGTH'        => 'Content-Length',
        # from here on blurry from memory: (and probably more to include as well..)
        'CONTENT_ENCODING'      => 'Content-Encoding',
        'CONTENT_TYPE'          => 'Content-Type',
);

my $headers;
foreach my $key (keys %env_to_httpheader) {
        if (exists $ENV{$key}) {
                # $headers->{ $env_to_httpheader{$key} } = $ENV{$key};
                # "The optional $header argument should be a reference to an HTTP::Headers object or a plain array reference of key/value pairs."
                push(@{ $headers }, $env_to_httpheader{$key});
                push(@{ $headers }, $ENV{$key});
        }
}