code: public static DropboxAuthentication build(String appKey, String appSecret) {
          DropboxClientBuilder builder = new DropboxClientBuilder(appKey, appSecret);
          builder.requestToken = builder.service.getRequestToken();
  
          return builder;
      }
docs: Build authenticator to application with specified appKey and appSecret.
  
  @param appKey    application key
  @param appSecret application secret
  
  @return authenticator
  
  @see DropboxAuthentication