PHP Random String Generator

rand_string.php

<?php
/**
   * Generate a random string, using a cryptographically secure
   * pseudorandom number generator (random_int)
   *
   * For PHP 7, random_int is a PHP core function
   * For PHP 5.x, depends on https://github.com/paragonie/random_compat
   *
   * @param int $length      How many characters do we want?
   * @param string $keyspace A string of all possible characters
   *                         to select from
   * @return bool|string
   */
  function randString(int $length, $keyspace = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ') {
    $pieces = [];
    $max = mb_strlen($keyspace, '8bit') - 1;

    try {
      for ($i = 0; $i < $length; ++$i) {
        $pieces [] = $keyspace[random_int(0, $max)];
      }
    } catch (Exception $e) {
      return FALSE;
    }

    return implode('', $pieces);
  }