PHP CURL网站登录

我想使用curl自动登录到一个网站。但该网站表示，必须在浏览器中启用cookie。我找了很多，但都找不到。如果有人能帮忙的话，

在网站帮助中搜索了很多之后，我发现该网站使用了两个cookie Moodlesession和sessionid。我不知道如何把它们卷起来。请帮忙。

表格如下：

<form action="http://site_name/login/index.php" method="post" id="login">
      <div class="loginform">
        <div class="form-label"><label for="username">Username</label></div>
        <div class="form-input">
          <input type="text" name="username" id="username" size="15" value="">
        </div>
        <div class="clearer"><!-- --></div>
        <div class="form-label"><label for="password">Password</label></div>
        <div class="form-input">
          <input type="password" name="password" id="password" size="15" value="">
          <input type="submit" value="Login">
          <input type="hidden" name="testcookies" value="1">
        </div>
        <div class="clearer"><!-- --></div>
      </div>
    </form>

我使用的curl脚本是：

<?php
    $username="myusername";
    $password="mypassword";
    $url="login_url";
    $cookie="cookie.txt";
    $postdata="username=".$username."&password=".$password;
    $ch = curl_init();
    curl_setopt ($ch, CURLOPT_URL, $url);
    curl_setopt ($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
    curl_setopt ($ch, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.6) Gecko/20070725 Firefox/2.0.0.6");
    curl_setopt ($ch, CURLOPT_TIMEOUT, 60);
    curl_setopt ($ch, CURLOPT_FOLLOWLOCATION, 0);
    curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt ($ch, CURLOPT_COOKIEJAR, $cookie);
    curl_setopt ($ch, CURLOPT_REFERER, $url);
    curl_setopt ($ch, CURLOPT_POSTFIELDS, $postdata);
    curl_setopt ($ch, CURLOPT_POST, 1);
    curl_setopt ($ch, CURLOPT_COOKIESESSION, true);
    curl_setopt ($ch, CURLOPT_COOKIEJAR, 'cookie.txt');
    $result = curl_exec ($ch);
echo $result;
curl_close($ch);

？>