private function GetHttpHeaderStrong()
    {
        $token = $this->_root->OAuthTokenManager->GetToken($this->GetAutenticationKey());

        if (is_null($token) || !isset($token->access_token) || !isset($token->token_type)) {
            throw new Exception('OAuth token is not created (or is invalid) for strong authentication');
        }

        return 'Authorization: ' . $token->token_type . ' ' . $token->access_token;
    }