public function post($data) {
    $email = $data->email;
    $password = $data->password;
    $username = explode('@', $data->email)[0];

    Drupal::logger('custom_rest-api')->notice('Received registration request for user with email: @email, password: @password, username: @username for data: @data',
    array(
        '@email' => $email,
        '@password' => $password,
        '@username' => $username,
        '@data' => $data
    ));