title: Access to XMLHttpRequest has been blocked by CORS policy
body: <p>I've a problem when I try to do PATCH request in an angular 7 web application.
  In my backend I have: </p>
  
  <pre class="lang-typescript prettyprint-override"><code>app.use((req, res, next) =&gt; {
      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();
  });
  </code></pre>
  
  <p>In my frontend service, I've:</p>
  
  <pre class="lang-typescript prettyprint-override"><code>  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) =&gt; res.json());
    };
  </code></pre>
  
  <p>The error is: </p>
  
  <pre><code>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.
  </code></pre>
  
  <p>What can I to do?
  Thanks.</p>