private function fetchAccessToken() {
        // Setup the params
        $params = [
            'client_id'     => $this->clientID,
            'client_secret' => $this->secret,
            'grant_type'    => 'authorization_code',
            'code'          => $this->requestToken
        ];

        if (isset($this->redirectURI)) {
            $params['redirect_uri'] = $this->redirectURI;
        }

        // Parse the cURL result
        $this->parseAccessToken(CURL::post($this->url, $params));
    }