public function createAuthHeader()
    {
        if ($this->timestamp === null) {
            $this->setTimestamp();
        }

        if (!$this->timestamp->isValid()) {
            throw new InvalidSignDataException('Timestamp is invalid. Too old?');
        }

        if ($this->nonce === null) {
            $this->nonce = new Nonce();
        }

        $auth_header =
            'EG1-HMAC-SHA256 ' .
            'client_token=' . $this->auth['client_token'] . ';' .
            'access_token=' . $this->auth['access_token'] . ';' .
            'timestamp=' . $this->timestamp . ';' .
            'nonce=' . $this->nonce . ';';

        return $auth_header . 'signature=' . $this->signRequest($auth_header);
    }