Logging in to a webpage through CURL, differently - php

Question

There's a webpage that I need to log in to. I used CURL with post to login, but it's not enough. When you log in from the website the post also includes a string that is always changing. Is threre a way to get over that?
I use this:
$ch = curl_init();
curl_setopt ($ch, CURLOPT_URL, $url);
curl_setopt ($ch, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows; U; Windows NT 5.1; he-IL; rv:1.8.1.6) Gecko/20070725 Firefox/2.0.0.6");
curl_setopt ($ch, CURLOPT_REFERER, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, TRUE);
curl_setopt($ch, CURLOPT_POST, TRUE);
$post = "username=$username&password=$password";
curl_setopt($ch, CURLOPT_POSTFIELDS, $post);
$result = curl_exec($ch);
$info = curl_getinfo($ch);
curl_close($ch);
It's like I need the code to actually go to the webpage and fill the form regularly.
I looked everywhere but all I could find was using post data.
Thanks!

Answer 1

To pass that you need to visit the page with the form, grab the field and then use it in POST request when you submit the form.
I suggest you visit the form page not only for that, but also for the following reasons (some of which can be used to figure people using automatic requests):
You recieve cookies
You don't fake referrer, you actually visited the page
You might want to check form fields to see if there's any new ones added since you wrote the script. That could be the case if form setup changes and you might want to adapt to that, if you don't then your script might stop working one day