原始碼如下：使用方法 `createProxyServer` 建立一個代理伺服器, 監聽在埠 8082 上，把請求傳送給 localhost:9000 上監聽的伺服器。

後者僅僅返回一個 request successfully proxied 的訊息給請求方。

```javascript
var http = require('http'),
    httpProxy = require('http-proxy');

httpProxy.createProxyServer({target:'http://localhost:9000'}).listen(8082);

http.createServer(function (req, res) {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.write('request successfully proxied!' + '\n' + JSON.stringify(req.headers, true, 2));
  res.end();
}).listen(9000);
```
遇到錯誤訊息：

> Access to XMLHttpRequest at 'http://localhost:8082/https://services.odata.org/V2/Northwind/Northwind.svc/$metadata?sap-language=EN' from origin 'http://localhost:8080' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

![](https://img-blog.csdnimg.cn/img_convert/7f4d39cebb0f8917945685ccbd913955.png)

# 解決方案

在 HTTP response 頭部欄位增添一條欄位："Access-Control-Allow-Origin": "*"

![](https://img-blog.csdnimg.cn/img_convert/026cc7f3ebffa632a346a3eafa550e0e.png)

重啟 proxy 伺服器之後，錯誤訊息變成了：

> Access to XMLHttpRequest at 'http://localhost:8082/https://services.odata.org/V2/Northwind/Northwind.svc/$metadata?sap-language=EN' from origin 'http://localhost:8080' has been blocked by CORS policy: Request header field maxdataserviceversion is not allowed by Access-Control-Allow-Headers in preflight response.

![](https://img-blog.csdnimg.cn/img_convert/9db325278f16ac15036c22bfe9fc03da.png)

解決辦法是，在 response 裡新增如下欄位：

```javascript
res.writeHead(200, { 'Content-Type': 'text/plain',
                        "Access-Control-Allow-Origin": "*",
                        "Access-Control-Allow-Headers": "*" });
```

修改之後問題消失：
![](https://img-blog.csdnimg.cn/img_convert/9c8db587ebc4c9c4932638ded3e0f75e.png)

SAP UI5 應用發起的 metadata 資料請求，被 proxy 伺服器成功攔截並返回：
![](https://img-blog.csdnimg.cn/img_convert/093afc4a0d7170873c5b900220084354.png)

> Error [ERR_TLS_CERT_ALTNAME_INVALID]: Hostname/IP does not match certificate's altnames: Host: localhost. is not in the cert's altnames: DNS:*.azurewebsites.net, DNS:*.scm.azurewebsites.net, DNS:*.azure-mobile.net, DNS:*.scm.azure-mobile.net, DNS:*.sso.azurewebsites.net
    at Object.checkServerIdentity (tls.js:287:12)
    at TLSSocket.onConnectSecure (_tls_wrap.js:1511:27)
    at TLSSocket.emit (events.js:315:20)
    at TLSSocket._finishInit (_tls_wrap.js:936:8)
    at TLSWrap.ssl.onhandshakedone (_tls_wrap.js:710:12) {
  reason: "Host: localhost. is not in the cert's altnames: DNS:*.azurewebsites.net, DNS:*.scm.azurewebsites.net, DNS:*.azure-mobile.net, DNS:*.scm.azure-mobile.net, DNS:*.sso.azurewebsites.net",
  host: 'localhost',

這個錯誤和這個 [StackOverflow](https://stackoverflow.com/questions/57766108/nodejs-express-reverse-proxy-tls-cert-altname-invalid-error) 討論相關。

程式碼也類似：

```javascript
var express = require('express');
var app = express();
var httpProxy = require('http-proxy');
var apiProxy = httpProxy.createProxyServer();
var serverOne = 'https://idena.navarra.es/ogc/wms?';

app.all('/idena', function (req, res) {
  apiProxy.web(req, res, {target: serverOne});
});

app.listen(3000, function () {
  console.log('Working!');
});
```

當請求傳送給 idena 時，代理伺服器試圖傳送往伺服器：https://idena.navarra.es/ogc/wms?

源伺服器是 HTTP，而目的伺服器是 HTTPS.

解決這個錯誤的辦法：在 proxy option 裡，指定下列這個選項：

```javascript
changeOrigin: true
```

![](https://img-blog.csdnimg.cn/img_convert/f9d27cf5086a729071f85170434bd35e.png)

重新 proxy 伺服器之後，問題消失：`ERR_TLS_CERT_ALTNAME_INVALID` 錯誤被修復了。
![](https://img-blog.csdnimg.cn/img_convert/909ffbb5d32a32a61ddadbda28e3372f.png)

但是這個錯誤訊息又回來了：

> http://localhost:8082/https://services.odata.org/V2/Northwind/Northwind.svc/$metadata?sap-language=EN' from origin 'http://localhost:8080' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

400 bad request:

![](https://img-blog.csdnimg.cn/img_convert/228e9f2a5d6981c9e61b3f61f9c3e483.png)

直接訪問這個 url：http://localhost:8082/https://services.odata.org/V2/Northwind/Northwind.svc/$metadata?sap-language=EN

會遇到如下錯誤：

![](https://img-blog.csdnimg.cn/img_convert/db8ec0f9b315e2fe5519934952352a62.png)

使用 http-proxy 代理 SAP UI5 應用發起的 HTTP 請求

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