CORS problem with Django, missing 'Access-Control-Allow-Headers'

Question

I'm having a problem with CORS and Django where, when I try to POST a JSON from my app, I get no response but got an error:

Cross-origin request blocked: Same Origin Policy prevents reading of remote resource at http://localhost:8000/converter2/. (Reason: 'access-control-allow-headers' symbol missing in 'Access-Control-Allow-Headers' CORS header during CORS pre-connection).

Also, when I try to connect my Django server logs this: "OPTIONS /converter2/ HTTP/1.1" 200 0. Okay, I'm not receiving 'Access-Control-Allow-Headers' from the server. From all I have read this needs to be solved in server side. So I tried to install django-cors-headers and configure it like the following:

# settings.py
INSTALLED_APPS = [
...
'corsheaders'
]
MIDDLEWARE = [
    'corsheaders.middleware.CorsMiddleware',
    ...
]
CORS_ORIGIN_ALLOW_ALL = True

Sadly nothing changed. So I tried change the CORS_ORIGIN_ALLOW_ALL to False and add my app origin to CORS_ORIGIN_WHITELIST, just like this:

CORS_ORIGIN_WHITELIST = [
    'http://localhost:8000'
]

Again, nothing changed. I tried now to force the headers with the server response, like suggested in this answer:

...
response = HttpResponse(status=201)
response["Access-Control-Allow-Origin"] = "*"
response["Access-Control-Allow-Headers"] = "X-Requested-With, Content-Type"
return response

Still nothing, I don't know what else I can try. I would appreciate new suggestions, thank you.

Ionic v4, port 8100

Django v2.2.4, port 8000

I don't think this is a front side problem, but I will post the request for reference:

const httpOptions = {
    headers: new HttpHeaders({
      'Content-Type':  'application/json',
      'Access-Control-Allow-Origin': 'http://localhost:8000, http://localhost:8100',
      'Access-Control-Allow-Methods': 'POST, GET, OPTIONS',
      'Access-Control-Allow-Headers': 'Content-Type',
      'Accept': 'application/json'
    })
};

this.http.post("http://localhost:8000/converter2/", file, httpOptions)
.pipe(
    finalize(() => {
        loader.dismiss();
    })
).subscribe(res => {
    if (res['success']) {
        this.presentToast('File uploaded complete')
    } else {
        this.presentToast('File uploaded failed')                       
    }
});

Answer 1

As stated by sideshowbarker, the problem in this particular case was that, in my app request, the headers configuration was incorrect. I was sending Access-Control-Allow-Origin, Access-Control-Allow-Methods and Access-Control-Allow-Headers inside request's headers, while the correct is receive this attributes from the response headers.

Some simple PHP servers don't thrown an error when this options are send, that is why I used them, but it's not the case with Django server. Nevertheless, don't send this headers as a request.

const httpOptions = {
    headers: new HttpHeaders({
      'Content-Type':  'application/json',
      'Accept': 'application/json'
    })
};