Get rid of CORS for method other than GET

[jbreizh]

Hello,
Just a quick note to fix CORS error especially for testing when you are developing your client (so local file on your computer) requesting on your ESP.

1. First solution, launching chromium without security (for exemple on linux) :

chromium --disable-web-security --user-data-dir=~/test

2. OR adding CORS (for all method) to the ESP !!!!!!

  // called when the url is not defined
  server.onNotFound([]() {
    if (server.method() == HTTP_OPTIONS)
    {
      server.sendHeader("Access-Control-Max-Age", "10000");
      server.sendHeader("Access-Control-Allow-Methods", "PUT,POST,GET,DELETE");
      server.sendHeader("Access-Control-Allow-Headers", "*");
      server.send(200);
    }
    else
    {
      handleFileRead(server.uri());
    }
  });
  
  // enable CORS header in webserver results
  server.enableCORS(true);

Quick explanation (i am not a pro at all):

• the server.enableCORS(true); support CORS for GET method, but not for POST
• When you send a POST request, the browser send a preflight with method OPTIONS and the ESP has to send a response to say what method he allows. That's the if (server.method() == HTTP_OPTIONS)
• After this preflight clearing CORS, you browser send finally its POST request

It take me a lot of time to understand, so i wanted to share this solution. If you have a better one, i am happy to hear you !!!!