how to read facebook signed_request to get user_id
facebook, facebook-app-requests, facebook-authentication, facebook-canvas, php
Solution
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
Problem
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 say that `signed_request` can be get through `$_POST['signed_request']` I agree its working for me. Now according to them if the user is logged in i will be getting a JSON object value like this:- ``` { "expires":UNIXTIME_WHEN_ACCESS_TOKEN_EXPIRES, "algorithm":"HMAC-SHA256", "issued_at":UNIXTIME_WHEN_REQUEST_WAS_ISSUED, "oauth_token":"USER_ACCESS_TOKEN", "user_id":"USER_ID", "user":{ "country":"ISO_COUNTRY_CODE", "locale":"ISO_LOCALE_CODE", ... } } ``` Now i want to fetch the `user_id` out of this so i am using this piece of code but its not working:- ``` if(isset($_POST['signed_request'])) { echo 'YES'; $json = $_POST['signed_request']; $obj = json_decode($json); print $obj->{'user_id'}; } ``` It just print the `YES`. Why is it so? I have read somewhere that without app authentication i will not be able to extract the `user_id` but according to the facebook, this is the 1st step and authenticating the application would be 4th. I am new to it, if somebody can please help me, it will be of great help. Thanks.