how to read facebook signed_request to get user_id

Question

According to Facebook - Authentication within a Canvas Page Document, they say that we will be getting a signed_request which consists a JSON object. Now they s

Answer 1

I think it failed at json_decode($json) because $json is not a valid json string, as you've mentioned in comment about print_r($_POST['signed_request']);.

According to Facebook - Authentication within a Canvas Page Document, the signed_request parameter is encoded and, parsing the signed_request string will yield a JSON object.

if you're using the PHP SDK, just as Abhishek said in the comment, $facebook->getSignedRequest(); will give you the decoded json.

look here for more details on the Signed Request