protected function expireAccessToken($accessToken)
    {
        // Expire access token
        $token = $this->accessTokenMapper->findBy([
            'access_token' => $accessToken
        ]);

        if (! $token) {
            throw new OutOfBoundsException('Access token not found.');
        }

        $token->setExpires(date("Y-m-d H:i:s", time()));

        $this->accessTokenMapper->update($token);
    }