Make HTTP POST request from Lightning Component

I want to make a post request to a server, using this code:

({
    start : function(component, event, helper) {
        var xhr = new XMLHttpRequest();
        var url = "https://site.com/service";
        xhr.open("POST", url, true);
        xhr.setRequestHeader("Content-Type", "application/json");
        xhr.setRequestHeader("Accept", "application/json");
        xhr.setRequestHeader("token", "xxxxxxxxxxxxxxxxxxxxxxx");
        xhr.onreadystatechange = function () {
            if (xhr.readyState === 4 && xhr.status === 200) {
                var json = JSON.parse(xhr.responseText);
                console.log(json);
            }
        };
        var data = JSON.stringify({
              "evse_id": "scscrfgdfsgdfsdsfdgfd", 
              "plug_id": 1,
              "id_tag": {
                "tag_id": "test", 
                "tag_type": "UID"
              },
              "provider_id": "QTEDFF",
              "session_id": "123456789"
            }

        );
        xhr.send(data);
    }
})

I added https://site.com/service in CSP Trusted Site Definition and in
CORS Whitelist Origins but it shows this error message:

Failed to load https://site.com/service: Request header field token is not allowed by Access-Control-Allow-Headers in preflight response.

Is it possible to invoke this method only from the Lightning Component or have I to do from an Apex Class?