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POFacebook Auth and CSRF mechanism
 

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    <p>I am currently building a website using facebook authentication. I am running locally and keep getting CSRF errors. I am trying to understand their CSRF protection mechanism:</p> <pre><code> $code = $_REQUEST["code"]; $_SESSION['state']= $_REQUEST['state'];//GETS SITE WORKING BUT UNSAFE!!!/// if(empty($code)) { $_SESSION['state'] = md5(uniqid(rand(), TRUE)); //CSRF protection $dialog_url = "http://www.facebook.com/dialog/oauth?client_id=" . $app_id . "&amp;redirect_uri=" . urlencode($my_url) . "&amp;state=" . $_SESSION['state']; echo("&lt;script&gt; top.location.href='" . $dialog_url . "'&lt;/script&gt;"); } if($_REQUEST['state'] == $_SESSION['state']) { </code></pre> <p>What happens is that it seems my $_REQUEST['state'] is set but my $_SESSION['state'] is not. Hence to get it working i have the line which sets both equal. My $code variable never seems to be empty hence a new $_SESSION['state' variable is never set.</p> <p>Firstly what is the role of $_REQUEST['code'] and where does this/is this variable come from/set?</p> <p>Any ideas how to fix this with my unsafe line of code?</p> <p>p.s I know I should use the FB sdk, but am learning web design/security so this is a good exercise to learn how it works!!</p> <p>Many Thanks Sam</p> <hr> <p>To anybody who is interested, I have worked out how it works, but still haven't fixed my problem...Anyway</p> <p>The CSFR protection system works by saving a State 'ID' on the server-side in the $_SESSION['state'], the same ID is saved also inside the $_REQUEST['state'] , so on the client side. This therefore means if a CSRF attack occurs, the state value of the CSRF attack (client side) won't match that of $_SESSION['state'] hence the code does not proceed and the attack is prevented.</p> <p>Please correct me if I am wrong!</p>
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