Why Does Facebook\'s PHP SDK `getUser()` Method Return 0, and How Can I Fix It?

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

When attempting to retrieve the Facebook user ID using the getUser() method of the PHP SDK, many developers encounter the issue of constantly receiving the value 0. This problem arises despite properly authorizing the application through the login-button feature.

One possible cause of this issue lies in the framework's reliance on the $_REQUEST variable. However, the environment may not always automatically merge $_REQUEST with $_GET, $_POST, and $_COOKIE variables. This discrepancy can hinder the getCode() function's ability to retrieve the authorization code.

Solution:

To resolve this issue, modify the getCode() function in base_facebook.php 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']) {
            $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 ensures that the getCode() function properly checks for the authorization code in all possible request variables. After implementing this change, the getUser() method should correctly identify the logged-in Facebook user.

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