code: private static XeSource make(final Request req, final CharSequence app,
          final CharSequence rel, final CharSequence flag) throws IOException {
          return new XeLink(
              rel,
              new Href("https://github.com/login/oauth/authorize")
                  .with("client_id", app)
                  .with(
                      "redirect_uri",
                      new RqHref.Base(req).href()
                          .with(flag, PsGithub.class.getSimpleName())
                  )
          );
      }
docs: Ctor.
  @param req Request
  @param app Github application ID
  @param rel Related
  @param flag Flag to add
  @return Source
  @throws IOException If fails
  @checkstyle ParameterNumberCheck (4 lines)