Code to generate the one-time use password

gistfile1.php

function user_generate_token($username, $phoneNum, $method){
    global $accountsid, $authtoken, $fromNumber;

    /**
     * Create a store a temporary/one-time password. While session-based is ok for
     *  this proof of concept, to make this more secure we'd want to use a database,
     *  potentially a salt for the password, and some sort of timeout to expire the
     *  password of N minutes/hours. 
     */

    $password = substr(md5(time().rand(0, 10^10)), 0, 10);
    $_SESSION['password'] = $password;
    $_SESSION['username'] = $username;

    // Prepare the message with the password embedded
    $content = ('sms' == $method) ? "Your newly generated password is ".$password :
        "https://twimlets.com/message?Message%5B0%5D=Your%20newly%20generated%20password%20is%20%2C%2C" .
        urlencode(preg_replace("/(.)/i", "\${1},,", $password)) .
        "%20To%20repeat%20that%2C%20your%20password%20is%20%2C%2C" . urlencode(preg_replace("/(.)/i", "\${1},,", $password));
    $method  = ('sms' == $method) ? 'sms_messages' : 'calls';

    $client = new Services_Twilio($accountsid, $authtoken);
    // Send the message via SMS or Voice
    $item = $client->account->$method->create(
                $fromNumber,    // The Twilio number we're sending from
                $phoneNum,      // The user's phone number
                $content
            );
    $message = "A new password has been generated and sent to your phone number.";

    return $message;
}