Generate random password

/**
 * Generate a random character array from the list of $possible characters
 *
 * @param array  $possible Array of possible characters
 * @param int    $length   Length of string to generate
 * @return array An array of $length random characters
 */
function randomStringArray($possible, $length) {
    $stringArray = array();
    $possibleCount = count($possible);

    $i = 0;
    while ($i < $length) {
        // pick a random character from the possible ones
        $char = $possible[mt_rand(0, $possibleCount - 1)];

        // we don't want this character if it's already in the password
        if (!in_array($char, $stringArray)) {
            $stringArray[] = $char;
            $i++;
        }
    }

    return $stringArray;
}

/**
 * Generate password that contains 6 letters and 2 numbers
 */
function generatePassword() {
    $letters = array_merge(range('a', 'z'), range('A', 'Z'));
    $numbers = range('0', '9');
    $chars = array_merge(
        randomStringArray($letters, 6), randomStringArray($numbers, 2));
    shuffle($chars);
    return implode('', $chars);
}