Laravel

    public function user()
    {
        if ($this->user) {
            return $this->user;
        }

        if ($this->hasInvalidState()) {
            throw new InvalidStateException;
        }

        $response = $this->getAccessTokenResponse($this->getCode());

        $this->user = $this->mapUserToObject($this->getUserByToken(
            $token = Arr::get($response, 'access_token')
        ));

        return $this->user->setToken($token)
                    ->setRefreshToken(Arr::get($response, 'refresh_token'))
                    ->setExpiresIn(Arr::get($response, 'expires_in'));
    }

    protected function hasInvalidState()
    {
        //stateless()が呼び出されていればfalseが返る
        if ($this->isStateless()) {
            return false;
        }

        //セッションのstateを取得し削除
        $state = $this->request->session()->pull('state');
        //stateが空またはURLパラメータのstateと異なる場合trueを返す
        return empty($state) || $this->request->input('state') !== $state;
    }

    public function getAccessTokenResponse($code)
    {
        //https://github.com/login/oauth/access_tokenへリクエストしアクセストークンを取得する
        $response = $this->getHttpClient()->post($this->getTokenUrl(), [
            'headers' => ['Accept' => 'application/json'],
            'form_params' => $this->getTokenFields($code),
        ]);

        return json_decode($response->getBody(), true);
    }