public function getHeader() : string
    {
        $salt = $this->getEncodedSalt();
        $hmac = $this->getEncodedHMAC();

        if ($this->version === 2) {
            $data = \base64_encode(\json_encode([
                'access_token' => $this->token->accessToken,
                'date' => $this->date,
                'hmac' => $hmac,
                'salt' => $salt,
                'v' => 2
            ]));

            return "HMAC {$data}";
        }

        // The version 1 HMAC is returned by default
        return "HMAC {$this->token->accessToken},{$hmac},{$salt}";
    }