CORS错误：当通过nginx服务create-react应用程序时，无法在nodejs中调用express路由

由于CORS错误，当通过nginx服务create-react应用程序时，我无法在nodejs中调用express路由。我花了几个小时在谷歌上搜索这个问题，并查看堆栈溢出的帖子，但无法找到解决问题的方法。

我有一个react应用程序，我用npm run build构建了它。获取请求看起来像：

    let response;
    try {
        response = await fetch("https://www.mywebsite.com/api/signIn", {
            method: "POST",
            headers: {
                "Access-Control-Allow-Credentials": "true",
                "Content-Type": "application/json",
            },
            body: JSON.stringify(userLoginInfo),
            credentials: "include",
        });
    } catch (error) {
        ...
        return;
    }

我的快递服务器、cors设置和路线如下：

... redis configuration ...

const app = express();
app.use(express.json());
// if you run behind a proxy (e.g. nginx)
app.set("trust proxy", 1);

// setup CORS logic
const whitelist = new Set(["http://localhost:3000", "http://mywebsite.com", "https://mywebsite.com"
]);
const corsOptions = {
    optionsSuccessStatus: 200,
    origin: (origin, callback) => {
        console.log(origin);
        if (whitelist.has(origin)) {
            callback(null, true);
        } else {
            callback(new Error("Not allowed by CORS"));
        }
    },
    credentials: true,
};
app.options("*", cors(corsOptions)); // ??????????????
app.use(cors(corsOptions));
app.use(session);
app.use(router);
app.listen(8080, () => console.log("server is running on port 8080"));

router.post("/signIn", (req, res) => {
    const {email, password} = req.body;

    console.log(email, password);
    console.log(req.session);

    ... do stuff ...
});

我的nginx配置：

server {
    index index.html index.htm index.nginx-debian.html;
    server_name mywebsite.com www.mywebsite.com;

    #I've tried adding the following 3 lines - nothing changes
    #add_header 'Access-Control-Allow-Origin' 'http://localhost:3000' always;
    #add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS, PUT, DELETE' always;
    #add_header 'Access-Control-Allow-Headers' 'X-Requested-With,Accept,Content-Type, Origin' always;

    # react app & front-end files
    location / {
        root directoryToTheReactBuild/build;
        try_files $uri /index.html;
    }

    location /api/ {
        proxy_pass http://localhost:8080;
        proxy_buffering         on;
    }

    #managed by Certbot
    listen 443 ssl;
    ssl_certificate /etc/letsencrypt/live/mywebsite.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/mywebsite.com/privkey.pem;
    include /etc/letsencrypt/options-ssl-nginx.conf;
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem;
}

所以我在一个AWS EC2实例中完成这一切，并使用https访问我的网站。正如我所说，我已经构建了react应用程序，但我正在使用npm start运行express服务器，直到一切正常。我现在得到的错误是："Not allowed by CORS"，来自express应用程序。console.log中未定义原点。

有人能告诉我我做错了什么吗？