我从API收到的JSON字符串

{"accessTokenResponse":{"token":"562371e99fda4296a380547cb5bf9fab","token_type":"Bearer","expires_in_seconds":"77476","client_id":"LTcyMDI1NDI0OQ==","responseStatus":{"code":"100000","message":"Service operation completed successfully","messageDetails":"Access token assigned."}}}

我想提取的信息

562371e99fda4296a380547cb5bf9fab //-->The Token

我的尝试

<?php
    $user = "LTcyMDI1NDI0OQ==";
    $password = "MjAzMDI5MTU";
    $returnFormat = "json";
    $url = "https://sandbox.dhlecommerce.asia/rest/v1/OAuth/AccessToken?clientId=".$user.
    "&password=".$password."&returnFormat=".$returnFormat."";
    $method = "GET";
    $headers = array(
        "content-type: application/json",
    $curl = curl_init();
    curl_setopt_array($curl, array(
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_URL => $url,
        CURLOPT_CUSTOMREQUEST => $method,
        CURLOPT_HTTPHEADER => $headers,
    $response = curl_exec($curl);
    $err = curl_error($curl);   
    $result = json_decode($response);
    curl_close($curl);