Replicate Me Too component, or any ID-required non-contract component to a custom component

Thank you for all these information AdamA, everything is working almost perfectly fine, except for the last step, the actual "Add a me too".

I have successfully logged in in the name of the user, and have tested API calls through AJAX like fetching a given message (testing the read permissions), or editing an existing message (testing the writing permissions). Both of those calls worked well.

 As for the AJAX Post call to "/messages/id/<message-id>/ratings/key/question_metoo/ratings/add?rating.value=1" after successfully logging in, however, I keep getting the "Autorisation refusée" (Authorization refused) with a 303 code from the API.

The code is pretty straightforward : 

$.ajax({
  type: "POST",
  url: "/restapi/vc/authentication/sessions/login",
  data: ({
    "xslt":"json.xsl"
  }),
  success: function(loginResponse) {
    $.ajax({
      type: "POST",
      url: "/restapi/vc/messages/id/" + questionId + "/ratings/key/question_metoo/ratings/add?rating.value=1,
      data: ({
        "rating.value=1",
        "xslt":"json.xsl"
      }),
      success: function(meTooResponse) {
        console.log(meTooResponse.response);
      }
    });
  }
});

(We are using auto-cookie login, that's why we don't have to use the session_key after loging in).

As for permissions, I have authorized API Reading and Writing Permissions in the Admin of course (the two previous successful calls I made confirm that those settings are indeed active).

Do you know why I am getting this 303 error only for Adding a Me Too to a question ? Is there a setting I might have overlooked ? 

Thanks in advance for any help you can provide !

EDIT : To add more info to my post, I have also tried to make the call via the FreeMarker Rest API, and the result is the same, i.e. "Authorization Refused".