Keeping state of logged in users

Question

So I made a website and set up user registration. It's now possible to register and login correctly and encrypted. But how do I keep state of the users identity? Do I have to send POST data with every link?

EDIT: Using PHP. Users post and comment on content. Users have a public profile with links to all content.

Answer 1

If using PHP - use $_SESSION data crossed with a $_COOKIE. This should allow you to keep track of user identity without having to pass $_POST variables all over the place - using $_POST is very insecure.