dcp::Certificate certificate (dcp::file_to_string (certificate_file));
dcp::EncryptedKDM kdm = film->make_kdm (certificate, cpl, valid_from.get(), valid_to.get(), formulation);
kdm.as_xml (output);
dcp::Certificate certificate (dcp::file_to_string (certificate_file));
dcp::EncryptedKDM kdm = film->make_kdm (certificate, cpl, valid_from.get(), valid_to.get(), formulation);
kdm.as_xml (output);