public static function Login($username, $password) {
    $result = HelpersDatabase::get()->select("SELECT * FROM users WHERE user_username = :user_username", array(":user_username" => $username));

    if (empty($result)) {
        $response["error_message"] = "User does not exist";
    } else {
        if (password_verify($password, $result[0]->user_password)) {
            $response["success"] = true;
            HelpersSession::set("user", $result[0]->user_id);
        } else {
            $response["error_message"] = "Password invalid";
        }
    }

    echo json_encode($response);
}

$("#login_form").submit(function(e) {
e.preventDefault();

var username = $("input[name=username]").val();
var password = $("input[name=password]").val();

$.ajax({
    url: "login/authentificate",
    type: "POST",
    data: {username: username, password: password},
    success: function(response) {
        alert(response);
    },
    error: function(error) {
        console.log(error);
    }
});