Q:

Access to XMLHttpRequest has been blocked by CORS policy

I've a problem when I try to do PATCH request in an angular 7 web application.
In my backend I have: 
app.use((req, res, next) => {
    res.set({
        "Access-Control-Allow-Origin": "*",
        "Access-Control-Allow-Methods": "*",
        "Access-Control-Allow-Headers": "'Access-Control-Allow-Headers: Origin, Content-Type, X-Auth-Token'",
    });

    next();
});

In my frontend service, I've:
  patchEntity(ent: any, id) {
    let headers = new Headers({ 'Content-Type': '*' });
    let options = new RequestOptions({ headers: headers });
    return this.http.patch('my_url', ent).map((res: Response) => res.json());
  };

The error is: 
Access to XMLHttpRequest at 'my_url' from origin 'http://localhost:4200' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: It does not have HTTP ok status.

What can I to do?
Thanks.

A:

There are two ways this can be handled: 

Temporary Front-End solution so you can test if your API integration is working:

Click on window -> type run and hit enter -> in the command window copy: 
chrome.exe --user-data-dir="C://Chrome dev session" --disable-web-security
This will open a new "Chrome" window where you can work easily. This is a temporary solution. Every time you will have to work with this chrome window. 

Permanent solution:

In the backend code, the developer needs to add an annotation @Crossorigin right above the CRUD api call method. 
Let me know if it works. 

