src/Leevel/Session/Middleware/Session.php
protected function getSessionId(IRequest $request): ?string
    {
        return $request->cookies->get(
            $this->manager->getName(), null
        );
    }
protected function getSessionId(IRequest $request): ?string
    {
        return $request->cookies->get(
            $this->manager->getName(), null
        );
    }
获取 session ID.

@param \Leevel\Http\IRequest $request

@return null|string