yii/web/user.php 文件下的loginRequired 方法：重定向登录去掉$canRedirect判断就好
public function loginRequired($checkAjax = true, $checkAcceptHeader = true)

{
    $request = Yii::$app->getRequest();
    $canRedirect = !$checkAcceptHeader || $this->checkRedirectAcceptable();
    if ($this->enableSession
        && $request->getIsGet()
        && (!$checkAjax || !$request->getIsAjax())
        && $canRedirect
    ) {
        $this->setReturnUrl($request->getUrl());
    }
//  if ($this->loginUrl !== null && $canRedirect) {
    if ($this->loginUrl !== null ) {
        $loginUrl = (array) $this->loginUrl;
        if ($loginUrl[0] !== Yii::$app->requestedRoute) {
            return Yii::$app->getResponse()->redirect($this->loginUrl);
        }
    }
    throw new ForbiddenHttpException(Yii::t('yii', 'Login Required'));
}