Generate v4 UUID (requires PHP 7)

uuid.php

<?php
/*
 * this will generate a valid v4 UUID per Google's directive for use in the -sessiontoken- parameter
 */
function guidv4($data)
{
    assert(strlen($data) == 16);
    $data[6] = chr(ord($data[6]) & 0x0f | 0x40); // set version to 0100
    $data[8] = chr(ord($data[8]) & 0x3f | 0x80); // set bits 6-7 to 10

    $g = vsprintf('%s%s-%s-%s-%s-%s%s%s', str_split(bin2hex($data), 4));

    return $g;
}

$guuid =  guidv4(random_bytes(16));

?>