Getting curl to save cookies

What i need done is have curl post userID=john&password=abc123 , and any cookies that is set after that information is posted, then save them to cookie.txt

I assume you're using CURL because you want to post to another server?

Here is a good explanation of that part:
http://davidwalsh.name/execute-http-post-php-curl

If you're posting the form (username/password) to the same server,
Then I'm not sure why you're using CURL.

I think we need to know more before answering the cookie part, because
I'm not sure if cookies are the correct thing ... maybe PHP SESSION?
Or is there a MySQL database involved with the username/password?
How do you determine if the username and password is correct?