public function login($username, $accessKey)
    {
        // Do the challenge before loggin in
        if ($this->passChallenge($username) === false) {
            return false;
        }

        $postdata = [
            'operation' => 'login',
            'username'  => $username,
            'accessKey' => md5($this->serviceToken.$accessKey)
        ];

        $result = $this->sendHttpRequest($postdata);
        if (!is_array($result) || empty($result)) {
            return false;
        }

        // Backuping logged in user credentials
        $this->userName = $username;
        $this->accessKey = $accessKey;

        // Session data
        $this->sessionName = $result[ 'sessionName' ];
        $this->userID = $result[ 'userId' ];

        // Vtiger CRM and WebServices API version
        $this->vtigerApiVersion = $result[ 'version' ];
        $this->vtigerVersion = $result[ 'vtigerVersion' ];

        return true;
    }