Why Does Facebook\'s PHP SDK `getUser()` Always Return 0?

Why is Facebook PHP SDK getUser() Always Returning 0?

In developing web applications that interact with Facebook, the issue of getUser() consistently returning 0 is commonly encountered. This can hinder access to necessary user information and result in authentication errors.

One potential reason for this behavior lies in the PHP SDK's reliance on the $_REQUEST variable, which may not be merging correctly with other request variables ($_GET, $_POST, and $_COOKIE) in your environment. The PHP version can also play a role.

Inspecting the getCode() function within the base_facebook.php file reveals the following code:

protected function getCode() {
    if (isset($_REQUEST['code'])) {
        if ($this->state !== null &&
                isset($_REQUEST['state']) &&
                $this->state === $_REQUEST['state']) {

            // CSRF state has done its job, so clear it
            $this->state = null;
            $this->clearPersistentData('state');
            return $_REQUEST['code'];
        } else {
            self::errorLog('CSRF state token does not match one provided.');
            return false;
        }
    }

    return false;
}

To address this issue, we can modify this function as follows:

protected function getCode() {
    $server_info = array_merge($_GET, $_POST, $_COOKIE);

    if (isset($server_info['code'])) {
        if ($this->state !== null &&
                isset($server_info['state']) &&
                $this->state === $server_info['state']) {

            // CSRF state has done its job, so clear it
            $this->state = null;
            $this->clearPersistentData('state');
            return $server_info['code'];
        } else {
            self::errorLog('CSRF state token does not match one provided.');
            return false;
        }
    }

    return false;
}

This modification consolidates all request variables into the $server_info variable, which ensures that the getCode() function can access the code parameter from any of these sources, regardless of your PHP environment's configuration.

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