title: Flutter WebView with proxy
body: <p>I am trying to build app with webview that loads page with proxy. I need to change proxy programmatically (to set ip, port, username and password).</p>
  
  <p>I had an idea to use <strong>WebviewScaffold</strong> <em>(flutter_webview_plugin: ^0.3.0+2)</em> and to override globally <strong>HttpClient</strong> like this:</p>
  
  <pre><code>class CustomHttp extends HttpOverrides{
  
    @override
    HttpClient createHttpClient(SecurityContext securityContext){
      var client = new HttpClient();;
      client.findProxy = (Uri uri) {
        return 'PROXY XX.XX.XX.XX:{PORT};';
      };
      client.authenticate = (uri, scheme, realm) {
        client.addCredentials(uri, realm, new HttpClientBasicCredentials('username', 'password'));
      };
      return client;
    }
  
  }
  </code></pre>
  
  <p>but with no luck. Looks like WebviewScaffold is not using global HttpClient.</p>
  
  <p>Does anyone have an idea how can I can do this?</p>