@Override
  public void login(String username, File _privateKey) {
    String headlessChallenge = null;
    String decodedPwd = null;
    try {
      headlessChallenge = getHeadlessChallenge(username);
      decodedPwd = decodeHeadlessChallenge(headlessChallenge, _privateKey);
    } catch (Exception e) {
      logger.error("Unexpected error encountered while decoding headless challenge " + headlessChallenge + e.toString());
    }
    login(username, decodedPwd);
  }
Login using a private key
@param username The username of the user
@param _privateKey The path of the private key of the user
app/com/linkedin/drelephant/clients/azkaban/AzkabanWorkflowClient.java