Token generation function for Marketo REST API

marketo.php

define ("MKTO_HOST", "**Your Marketo host**");
define ("MKTO_CID", "**Your Marketo Client ID");
define ("MKTO_CS","**Your Marketo Client Seccret");

//generate token
function generate_token(){
    $ch = curl_init(MKTO_HOST . "/identity/oauth/token?grant_type=client_credentials&client_id=" . MKTO_CID . "&client_secret=" . MKTO_CS);
    curl_setopt($ch,  CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_HTTPHEADER, array('accept: application/json',));
    $response = json_decode(curl_exec($ch));
    curl_close($ch);
    $token = $response->access_token;
    return $token;
}