Passing POST headers through WebResourceRequested and CreateWebResourceRequest content is null exception

I want to be able to give GET and POST headers for specific URLs in our software. I've seen that passing GET headers and parameters is pretty easy. I though the same would be the case for POST headers, but no.

private void CoreWebView2_WebResourceRequested(object sender, CoreWebView2WebResourceRequestedEventArgs e)
{
    ICS_WebIntegratie webLink = _webView2WebLinkVM.CurrentWebObject;
    if (webLink != null && BaseUtil.IsFilledCollection(webLink.HeaderParameters))
    {
        foreach (ICS_WebHeaderParameter item in webLink.HeaderParameters)
        {
            if (item.HeaderTypeId == e.Request.Method || item.HeaderTypeId == WebIntegratie_DD.HEADERPARAM_VELD_Type_BOTH)
            {
                e.Request.Headers.SetHeader(item.Name, item.Value);
            }
        }
    }
}

A ICS_WebHeaderParameter can be POST, GET or both. In the case of GET, everything works like a charm. But in case of POST, the POST headers which are added to e.Equest.Headers are not received.

I saw that there was an alternative solution, which is to use WebView2.CoreWebView2.Environment.CreateWebResourceRequest(). The problem I am encountering with that is that the value for content is always unacceptable. If I add a portion to the above code, e.g.:

if (e.Request.Method == WebIntegratie_DD.HEADERPARAM_VELD_Type_POST)
{
    string headers = string.Empty;
    foreach (System.Collections.Generic.KeyValuePair<string, string> item in e.Request.Headers)
    {
        headers += $"{item.Key}: {item.Value}\n";
    }

    foreach (ICS_WebHeaderParameter item in webLink.HeaderParameters)
    {
        if (item.HeaderTypeId == e.Request.Method || item.HeaderTypeId == WebIntegratie_DD.HEADERPARAM_VELD_Type_BOTH)
        {
            headers += $"{item.Name}: {item.Value}\n";
        }
    }

    UTF8Encoding encoding = new UTF8Encoding();
    byte[] postdata = encoding.GetBytes("test");
    Stream stream = new MemoryStream(postdata);
    CoreWebView2WebResourceRequest req = (sender as WebView2Wpf.WebView2).CoreWebView2.Environment.CreateWebResourceRequest(e.Request.Uri, e.Request.Method, stream, headers);
    (sender as WebView2Wpf.WebView2).CoreWebView2.NavigateWithWebResourceRequest(req);
    return;
}

I always get a 'System.NullReferenceException' when the variable 'stream' is not null for example.

How can I pass POST HTTP headers to my web requests?

AB#38844414

Start with the CoreWebView2_WebResourceRequested handler and the CreateWebResourceRequest and NavigateWithWebResourceRequest calls shown in the issue. Reproduce the NullReferenceException with a non-null MemoryStream and inspect how POST headers and content are passed. Done means identifying the supported way to preserve POST content while adding headers, or documenting the limitation and workaround.