CORS：对预检请求的响应未通过访问控制检查：否'Access-Control-Allow-Origin'

Question

I'm trying to login to moodle from an external webpage using a post form to moodle, I used the next ajax to send the inputs:

var frm = $('#loginForm');

frm.submit(function(e) {
    e.preventDefault();
    $.ajax({
        type: frm.attr('method'),
        url: frm.attr('action'),
        data: frm.serialize(),
        xhrFields:{
            withCredentials:true
        },
        async:true,
        beforeSend: function (xhr){
            xhr.setRequestHeader('Access-Control-Allow-Origin', '*');
        },
        success: function (data) {
            console.log("Logged");
        },
        error: function (data) {
            console.log("NOT Logged");
        },
    });
});

Now into the moodle's login/index.php I insert the headers to make possible the CORS connection:

header("Access-Control-Allow-Credentials: true");
header("Access-Control-Allow-Origin: http://fabianmurillo.000webhostapp.com");
header("Origin" : "http://fabianmurillo.000webhostapp.com");

When I run the code, the browser returns an error:

..preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin'.. 

enter image description here

Dunno why browser is blocking the connection for login to moodle.

Thanks for your help.