code: public DataSiftConfig auth(String username, String apiKey) {
          if (username == null || apiKey == null || username.isEmpty() || apiKey.isEmpty()) {
              throw new IllegalArgumentException(String.format("A valid username and API key are required. Username = " +
                      "%s, API key = %s", username, apiKey));
          }
          this.username = username;
          this.apiKey = apiKey;
          return this;
      }
docs: /*
  Provide the user credentials that should be used for authentication
  
  @param username the DataSift username
  @param apiKey   the DataSift API key
  @return this object for further configuration