docs: public void addHeader(String key, String value) {
          if (key.equals("As-User")) {
              for (int i = 0; i < this.headers.size(); i++) {
                  if (this.headers.get(i).getKey().equals("As-User")) {
                      this.headers.remove(i);
                  }
              }
          }
          if (key.equals("X-Box-UA")) {
              throw new IllegalArgumentException("Altering the X-Box-UA header is not permitted");
          }
          this.headers.add(new RequestHeader(key, value));
      }