PHP: Caot login to another website using curl

I'm trying to login to an exteal website (https://eclass.aueb.gr) using curl but I can't. I tried using those functions which I found online with no success.

<?php
function login($url,$data){
    $fp = fopen("cookie.txt", "w");
    fclose($fp);
    $login = curl_init();
    curl_setopt($login, CURLOPT_COOKIEJAR, "cookie.txt");
    curl_setopt($login, CURLOPT_COOKIEFILE, "cookie.txt");
    curl_setopt($login, CURLOPT_TIMEOUT, 40000);
    curl_setopt($login, CURLOPT_RETURNTRANSFER, TRUE);
    curl_setopt($login, CURLOPT_URL, $url);
    curl_setopt($login, CURLOPT_USERAGENT, $_SERVER['HTTP_USER_AGENT']);
    curl_setopt($login, CURLOPT_FOLLOWLOCATION, TRUE);
    curl_setopt($login, CURLOPT_POST, TRUE);
    curl_setopt($login, CURLOPT_POSTFIELDS, $data);
    ob_start();
    retu curl_exec ($login);
    ob_end_clean();
    curl_close ($login);
    unset($login);    
}                  

function grab_page($site){
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
    curl_setopt($ch, CURLOPT_USERAGENT, $_SERVER['HTTP_USER_AGENT']);
    curl_setopt($ch, CURLOPT_TIMEOUT, 40);
    curl_setopt($ch, CURLOPT_COOKIEFILE, "cookie.txt");
    curl_setopt($ch, CURLOPT_URL, $site);
    ob_start();
    retu curl_exec ($ch);
    ob_end_clean();
    curl_close ($ch);
}

function post_data($site,$data){
    $datapost = curl_init();
        $headers = array("Expect:");
    curl_setopt($datapost, CURLOPT_URL, $site);
        curl_setopt($datapost, CURLOPT_TIMEOUT, 40000);
    curl_setopt($datapost, CURLOPT_HEADER, TRUE);
        curl_setopt($datapost, CURLOPT_HTTPHEADER, $headers);
    curl_setopt($datapost, CURLOPT_USERAGENT, $_SERVER['HTTP_USER_AGENT']);
    curl_setopt($datapost, CURLOPT_POST, TRUE);
    curl_setopt($datapost, CURLOPT_POSTFIELDS, $data);
        curl_setopt($datapost, CURLOPT_COOKIEFILE, "cookie.txt");
    ob_start();
    retu curl_exec ($datapost);
    ob_end_clean();
    curl_close ($datapost);
    unset($datapost);    
}

I'm trying to login using

login("https://eclass.aueb.gr/","uname=MYUSERNAME&pass=MYPASS&submit=");

and then grab the main page using

echo grab_page("https://eclass.aueb.gr/main/portfolio.php");

Is there anything wrong with the code? I get nothing as a result and the cookie.txt file stays empty.