Facebook generates a token that never expires - PHP

facebookToken.php

public function getNeverExpireToken($token)
{
    $clientId = FB_APP_ID;
    $clientSecret = FB_APP_SECRET;

    //long lived token :
    $apiUrl = "https://graph.facebook.com/v3.0";
    $apiToken = "$apiUrl/oauth/access_token?grant_type=fb_exchange_token&client_id=$clientId&client_secret=$clientSecret&fb_exchange_token=$token";
    $response = file_get_contents($apiToken);
    $longLiveToken = json_decode($response)->access_token;

    // user id :
    $apiUser = "$apiUrl/me?access_token=$longLiveToken";
    $responseUser = file_get_contents($apiUser);
    $idUser = json_decode($responseUser)->id;

    // never expires token :
    $apiPermaToken = "$apiUrl/$idUser/accounts?access_token=$longLiveToken&fields=access_token,name,id,instagram_business_account";
    $responsePermaToken = file_get_contents($apiPermaToken);

    $data = json_decode($responsePermaToken)->data;

    // get tokens :
    foreach ($data as $el) {
        $name = $el->name;
        $id = $el->id;
        $token = ['access_token' => $el->access_token];
    }
}