https://medium.com/@sirajul.anik/omc-oh-my-cors-4046ad22c242

requests.js

function parser(url) {
    return url.replace(/^\/(.*)$/g, '$1');
}

HOST = 'http://127.0.0.1:8080/';

function get(url = '/get') {
    fetch(HOST + parser(url), {
        method: 'GET',
    }).then((data) => data.json()).then((data) => console.log(data));
}

function cget(url = '/get') {
    fetch(HOST + parser(url), {
        method: 'GET',
        credentials: "include",
    }).then((data) => data.json()).then((data) => console.log(data));
}

function get_header(url = '/get') {
    fetch(HOST + parser(url), {
        method: 'GET',
        headers: {
            'X-ALLOWED-1': 'allowed-1',
            "Content-Type": "application/text",
            'authorization': 'bearer auth-token'
        },
        credentials: "include",
    }).then((data) => data.json()).then((data) => console.log(data));
}

function head(url = '/head') {
    fetch(HOST + parser(url), {
        method: 'HEAD',
    }).then((data) => console.log('head request sent'));
}


function post(url = '/post') {
    fetch(HOST + parser(url), {
        method: "POST",
        body: JSON.stringify({'post-field-1': 1, 'post-field-2': 2}),
    }).then((data) => data.json()).then((data) => console.log(data));
}

function cpost(url = '/post') {
    fetch(HOST + parser(url), {
        method: "POST",
        body: JSON.stringify({'post-field-1': 1, 'post-field-2': 2}),
        credentials: "include"
    }).then((data) => data.json()).then((data) => console.log(data));
}

function post_header(url = '/post') {
    fetch(HOST + parser(url), {
        method: "POST",
        body: JSON.stringify({'post-field-1': 1, 'post-field-2': 2}),
        headers: {
            'X-ALLOWED-1': 'allowed-1',
            "Content-Type": "application/text",
            'authorization': 'bearer auth-token'
        },
        credentials: "include"
    }).then((data) => data.json()).then((data) => console.log(data));
}

function put(url = '/put') {
    fetch(HOST + parser(url), {
        method: "PUT",
        body: JSON.stringify({'PUT-field-1': 1, 'PUT-field-2': 2}),
    }).then((data) => data.json()).then((data) => console.log(data));
}

function cput(url = '/put') {
    fetch(HOST + parser(url), {
        method: "PUT",
        body: JSON.stringify({'PUT-field-1': 1, 'PUT-field-2': 2}),
        credentials: "include"
    }).then((data) => data.json()).then((data) => console.log(data));
}

function put_header(url = '/put') {
    fetch(HOST + parser(url), {
        method: "PUT",
        body: JSON.stringify({'PUT-field-1': 1, 'PUT-field-2': 2}),
        headers: {
            'X-ALLOWED-1': 'allowed-1',
            "Content-Type": "application/text",
        },
        credentials: "include"
    }).then((data) => data.json()).then((data) => console.log(data));
}

function patch(url = '/patch') {
    fetch(HOST + parser(url), {
        method: "PATCH",
        body: JSON.stringify({'patch-field-1': 1, 'patch-field-2': 2}),
        credentials: "include"
    }).then((data) => data.json()).then((data) => console.log(data));
}

function cpatch(url = '/patch') {
    fetch(HOST + parser(url), {
        method: "PATCH",
        body: JSON.stringify({'patch-field-1': 1, 'patch-field-2': 2}),
    }).then((data) => data.json()).then((data) => console.log(data));
}

function patch_header(url = '/patch') {
    fetch(HOST + parser(url), {
        method: "PATCH",
        body: JSON.stringify({'patch-field-1': 1, 'patch-field-2': 2}),
        headers: {
            'X-ALLOWED-1': 'allowed-1',
            "Content-Type": "application/text",
        },
        credentials: "include"
    }).then((data) => data.json()).then((data) => console.log(data));
}

function del(url = '/delete') {
    fetch(HOST + parser(url), {
        method: "DELETE",
        body: JSON.stringify({'delete-field-1': 1, 'delete-field-2': 2}),
    }).then((data) => data.json()).then((data) => console.log(data));
}

function cdel(url = '/delete') {
    fetch(HOST + parser(url), {
        method: "DELETE",
        body: JSON.stringify({'delete-field-1': 1, 'delete-field-2': 2}),
        credentials: "include"
    }).then((data) => data.json()).then((data) => console.log(data));
}

function del_header(url = '/delete') {
    fetch(HOST + parser(url), {
        method: "DELETE",
        body: JSON.stringify({'delete-field-1': 1, 'delete-field-2': 2}),
        headers: {
            'X-ALLOWED-1': 'allowed-1',
            "Content-Type": "application/text",
        },
        credentials: "include"
    }).then((data) => data.json()).then((data) => console.log(data));
}
// post()
// post('/post-method')
// cpost()
// post_header()
// User SERVER TERMINAL to view the passed values

server.py

#!/usr/bin/env python
# Reflects the requests from HTTP methods GET, POST, PUT, and DELETE
# Written by Nathan Hamiel (2010)

# Cloned & Updated from: https://gist.github.com/1kastner/e083f9e813c0464e6a2ec8910553e632
import json
from http.server import HTTPServer, BaseHTTPRequestHandler
from optparse import OptionParser

allow = False
port = 8080


class RequestHandler(BaseHTTPRequestHandler):

    def log_message(self, format, *args):
        pass

    def process_request(self):
        request_path = self.path
        method = self.command.upper()

        request_headers = self.headers
        content_length = request_headers.get('Content-Length')
        length = int(content_length) if content_length else 0

        data = {
            'path': request_path,
            'method': method,
            'content-length': content_length,
            'headers': dict(request_headers),
            'data': json.loads(str(self.rfile.read(length).decode('ascii')) or '{}')
        }
        print(json.dumps(data, indent=2))

        self.send_response(200)
        self.send_header("Content-Type", "application/json")

        if allow:
            self.send_header('ACCESS-CONTROL-ALLOW-CREDENTIALS', 'true')
            self.send_header('ACCESS-CONTROL-ALLOW-HEADERS',
                             'Authorization, X-ALLOWED-1, '
                             'X-ALLOWED-2, X-ALLOWED-3, Content-Type')  # * or Comma separated values
            self.send_header('ACCESS-CONTROL-ALLOW-METHODS', 'DELETE, PATCH, POST, GET')  # * or Comma separated values
            self.send_header('ACCESS-CONTROL-ALLOW-ORIGIN', 'chrome-search://local-ntp')  # * or Comma separated values
            self.send_header('ACCESS-CONTROL-EXPOSE-HEADERS', '*')  # * or Comma separated values
            self.send_header('Set-Cookie', 'id=a3fWa; Expires=Wed, 21 Oct 2021 07:28:00 GMT')
            # self.send_header('ACCESS-CONTROL-MAX-AGE', 600)  # seconds

        self.end_headers()
        self.wfile.write(bytes(json.dumps({
            'error': False,
            'message': 'Handled ' + method + ' request',
        }), 'utf-8'))

    def serve_get(self):
        request_path = self.path

        if request_path == '/favicon.ico':
            # Don't serve favicon
            self.send_response(200)
            self.end_headers()
            return

        self.process_request()

    def serve_post(self):
        self.process_request()

    def serve_options(self):
        self.process_request()

    do_GET = serve_get
    do_HEAD = serve_get
    do_DELETE = serve_post
    do_POST = serve_post
    do_PUT = serve_post
    do_PATCH = serve_post
    do_OPTIONS = serve_options


def main():
    print('Listening on 0.0.0.0:%s - %s CORS' % (port, 'ALLOWS' if allow else 'DISALLOWS'))
    server = HTTPServer(('', port), RequestHandler)
    server.serve_forever()


if __name__ == "__main__":
    parser = OptionParser()
    parser.usage = "Creates an http-server that will echo out HEAD, GET, POST, PUT, PATCH, DELETE in JSON format"
    parser.add_option('-a', '--allow', default='no')
    parser.add_option('-p', '--port', default=8080)
    (options, args) = parser.parse_args()

    if options.allow.lower()[0] == 'y':
        allow = True

    port = int(options.port)

    main()

# Commands to run
# python server.py --port 8090
# python server.py --allow y
# python server.py --allow y --port 8080