Cross origin POST request not working for Outlook API

Question

I'm using this part of the Outlook API. It says that you should be able to do a post request, however when I try I get the following error:

Failed to load https://login.microsoftonline.com/common/oauth2/v2.0/token: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:3003' is therefore not allowed access. The response had HTTP status code 400.

How do I fix this though? I obviously don't have access to Outlook's servers, but surely they would let me do a post request considering that's what it says to do in the documentation!.

Here is my code by the way if that helps:

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script>
  let url = new URL(window.location);
  let code = url.searchParams.get('code');
  let redirect = 'http%3A%2F%2Flocalhost%3A3003%2Fauth-process-token.html';
  let clientId = '<MY ID>';
  let clientSecret = '<MY KEY>';

  var req_string = 'grant_type=authorization_code&code=' + code + '&redirect_uri=' + redirect + '&client_id=' + clientId + '&client_secret=' + clientSecret;

  $.ajax({
    type: 'POST',
    url: 'https://login.microsoftonline.com/common/oauth2/v2.0/token',
    crossDomain: true,
    data: req_string,
    dataType: 'application/x-www-form-urlencoded',
    success: function (responseData, textStatus, jqXHR) {
      var value = responseData.someKey;
    },
    error: function (responseData, textStatus, errorThrown) {
      console.log('POST failed.', errorThrown);
    }
  });
</script>

EDIT: I fixed the "bad request" error, but it still gives me the other one.

Answer 1

One workaround for this is by using cors.io

http://cors.io/?http://your_link

so it would be

http://cors.io/?https://login.microsoftonline.com/common/oauth2/v2.0/token