generate random string via php - used https://packagist.org/packages/voku/portable-utf8 (UTF8::strlen)

randomstring.php

<?php

/**
 * generate random string
 *
 * @param string $len        length of the random string
 * @param string $characters characters string for the random selection
 *
 * @return string
 */
function randomString($len, $characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789')
{
  $len = (int)$len;
  $charLength = UTF8::strlen($characters) - 1;
  $string = '';

  if ($len > 0) {
    while ($len--) {
      $string .= $characters[mt_rand(0, $charLength)];
    }
  }

  return $string;
}