PHP - set session variable on form submit

I have a form on my page, and I want to send the user to the 'private' part of the page when they've submitted the开发者_开发百科 form.

I want to achieve this by using sessions, but I can't find out how to set a session variable when the form is submitted. This is because the form action is an external page, and when it has been submitted it gets sent back to the page where the form is. The problem is however that I cannot catch that with HTTP_REFERER because it's an https page.

So i have no idea how to do this. Anybody? Thx!

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A couple ways I can think of doing this:

1. Send the form to a local page that sets the session variable and then fopen()'s the remote page. Here's a post describing how to send POST data with PHP streams.

2. Use AJAX and the onbeforesubmit JavaScript hook. Basically, when the user clicks submit, cancel the form submission, send your AJAX request to your own server, then when it returns, submit the form. Make sure to disable the form submit button when you do this, as it could take some time for the round trip to your server.