Post multipart/form-data with Mojo::UserAgent

post.pl

# Trying to copy this Ruby example:
#RestClient.post('https://ME%40TEST.COM:SECRET@www.documentcloud.org/api/upload.json',
#:file   => File.new('/full/path/to/document/document.pdf','rb'),
#:title  => "2008 Blagojevich Tax Return",
#:source => "U.S. Attorney's Office",
#:access => 'private',
#:data   => {"date" => "2009-04-01", "exhibit" => "E1146"}
#)

my $ua = Mojo::UserAgent->new;
my $tx = $ua->post(
    'user:password@www.documentcloud.org/api/upload.json' =>
        form => {
        file => 'http://www.openinfo.gov.bc.ca/local/ibc/docs/Part%202.pdf',
        title =>
            'Review of the Draft Multicultural Strategic Outreach Plan, Part 2'
        }
);

if (my $res = $tx->success) { say $res->body }
else {
    my ($err, $code) = $tx->error;
    say $code ? "$code response: $err" : "Connection error: $err";
}

# Keep getting: 400 response: Bad Request