public function setDefaultAccessToken($token)
    {
        if (is_string($token)) {
            $this->accessToken = new AccessToken(json_decode($token, true));
        } elseif ($token instanceof AccessToken) {
            $this->accessToken = $token;
        } else {
            throw new \Exception("Incorrect access token");
        }
        if ($this->accessToken->hasExpired()) {
            $this->refreshToken();
        }
        return $this->accessToken;
    }