code: private static Request make(final Identity identity, final String header,
          final Request req) throws IOException {
          return new RqWithHeader(
              req,
              header,
              new Utf8String(new CcPlain().encode(identity)).asString()
          );
      }
docs: Ctor.
  @param identity Identity
  @param header Header name
  @param req Request
  @return Request
  @throws IOException If fails