Password logger for wordpress

gistfile1.php

<?php
/*
Password logger for wordpress
*/

function log_login_success($username) {
  log_login_attempts($username, true);
}
function log_login_fail($username) {
  log_login_attempts($username, false);
}

/**
 * Logs all login attempts to file while not storing successful
 * login passwords.
 * @param username is username field
 * @success boolean whether the login was successful or not
 */
function log_login_attempts($username, $success) {
  if (!empty($_POST)) {
    // EDIT LINE BELOW: change to full path of log destination
    $logFile = $_SERVER['DOCUMENT_ROOT'] . '/wp-content/themes/THEME/changelog.txt';

    // Start with current date and IP of user
    $log = array(
      date('Y-m-d H:i:s'),
      $_SERVER['REMOTE_ADDR'],
      sanitize_log_output($_POST['log']),
      (
        // Don't show successful login passwords in log
        $success ? 'SUCCESS'
        : sanitize_log_output($_POST['pwd'])
      )
    );
  
    $fh = fopen($logFile, 'a+');
    fputcsv($fh, $log);
    fclose($fh);
  }
  return $user;
}

/**
 * Simple sanitization for log output.
 */
function sanitize_log_output($out) {
  $out = str_replace("\n", '\\n', $out);
  $out = str_replace("\r", '\\r', $out);
  $out = str_replace("\t", '\\t', $out);
  return $out;
}
?>

Hello. How do I use this code?