How Can I Accurately Determine User Affinity for My Facebook Page Using the API?

Determining User Affinity for Your Facebook Page or URL

To ascertain whether a user has indicated interest in your Facebook page or a particular URL, Facebook's API provides a straightforward solution. However, there have been instances of confusion and unexpected results.

Let's delve into an example that initially yielded unsuccessful outcomes:

FB.api({
    method:     "pages.isFan",
    page_id:        my_page_id,
},  function(response) {
        console.log(response);
        if(response){
            alert('You Likey');
        } else {
            alert('You not Likey :(');
        }
    }
);

Contrary to expectations, this code returned a false flag even though the user in question had indeed expressed interest (i.e., they had liked the page).

The caveat lies in the requirement for an extended permission. If such permission has not been granted, the code will not accurately reflect the user's affinity.

Fortunately, there is an alternative approach that relies on OAuth 2.0 for Canvas and the $_REQUEST variable. By parsing the signed request, we can procure information about the user, including their page interaction status:

function parsePageSignedRequest() {
    if (isset($_REQUEST['signed_request'])) {
      $encoded_sig = null;
      $payload = null;
      list($encoded_sig, $payload) = explode('.', $_REQUEST['signed_request'], 2);
      $sig = base64_decode(strtr($encoded_sig, '-_', '+/'));
      $data = json_decode(base64_decode(strtr($payload, '-_', '+/'), true));
      return $data;
    }
    return false;
  }
  if($signed_request = parsePageSignedRequest()) {
    if($signed_request->page->liked) {
      echo "This content is for Fans only!";
    } else {
      echo "Please click on the Like button to view this tab!";
    }
  }

By implementing this method, you can accurately determine whether a user has interacted with your page or URL, providing a more reliable indication of their preference.

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