Curl - Executing php and get api response

Question

I am trying to make a restricted webpage. I want to execute a remote php file which contains api information and curl code.

Here's my first code (restrict.php):

<?php 
    if (!empty($_POST['invitation_code']) ) {   
    $invitation_code = $_POST['invitation_code'];
    $url = 'http://localhost/auth.php?invitation_code='.$invitation_code;

    $ch = curl_init();

    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($ch, CURLOPT_FRESH_CONNECT, true);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_HEADER, false);
    curl_setopt($ch, CURLOPT_URL, $url);

    curl_exec($ch);
    curl_close($ch);
    }   
?>

Here's auth.php:

<?php
if (!empty($_GET['invitation_code']) ) {    
    $invitation_code = $_GET['invitation_code'];
    $url = 'https://reqres.in/api/users/'.$invitation_code;
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_URL,$url);
    $resultauth=curl_exec($ch);
    curl_close($ch);
    var_dump(json_decode($resultauth, true));
    $result = file_get_contents($url);
    $myFile = "testFile.txt";
    $fh = fopen($myFile, 'w') or die("can't open file");
    $stringData = $result;
    fwrite($fh, $stringData);
    fclose($fh);
}

I want to execute auth.php using curl from the first script and auth.php should work in background

Problems:

1) restrict.php is waiting for auth.php to execute. auth.php is not running in background.

2) auth.php is too slow and is responding after like 1 minute.

Any ideas what could solve my problem?

Thanks!