* instance of this class may operate without a user, or on behalf of many users. Use the Slack API
 * dashboard to create a client ID and secret for this application.
 *
 * <p>You must configure your Slack API OAuth and Permissions page with a localhost URL like {@code
 * http://localhost:53203/oauth/}, passing the same port to this class’ constructor.
 */
public final class SlackApi {
  private final HttpUrl baseUrl = HttpUrl.get("https://slack.com/api/");

  private static final Interceptor REWRITE_CACHE_CONTROL_INTERCEPTOR = chain -> {
    Response originalResponse = chain.proceed(chain.request());
    return originalResponse.newBuilder()
        .header("Cache-Control", "max-age=60")
        .build();
  };

  private final OkHttpClient client;

  public RewriteResponseCacheControl(File cacheDirectory) throws Exception {
    Cache cache = new Cache(cacheDirectory, 1024 * 1024);