use DateTime::Format::RFC3339 qw();
use DateTime::Format::Strptime qw();
print DateTime::Format::RFC3339
    ->new
    ->format_datetime(DateTime::Format::Strptime
        ->new(
            locale => 'en',
            pattern => '%a %b %d %T %Y',
            on_error => 'croak',
        )->parse_datetime('Fri Jun 16 18:04:03 2012')
    );
# '2012-06-16T18:04:03+00:00'