<div class="boton" style="width: 100px; height: 100px;" onclick="login();">
                Entrar
            </div>

function login() {
var email = document.getElementById("email").value;
var password = document.getElementById("pass").value;
$.ajax({
    url : "/sistema/backend/public/login.php",
    type : "POST",
    data : {
        email : email,
        password : password
    },
    success : function(data) {
        if (data === "true") {
        location.href = "/sistema/view/principal/index.php";
        } else {
            document.getElementById("messages").style.border = "red solid 1px";
            document.getElementById("messages").style.background = "#e64943";
            $("#messages").html(data);
            document.getElementById("messages").style.display = "block";
        }
    }

<?php session_start();
require_once ($_SERVER['DOCUMENT_ROOT']."/sistema/backend/conection/conection.php");

if (isset($_POST["email"]) && isset($_POST["password"])) {
$conn = new ConnectionDBTvsystem();
$user = $conn -> getUsuario($_POST["email"], $_POST["password"]);

if (!is_null($user)) {
    $_SESSION['user'] = get_object_vars($user);
    echo "true";

} else{
    die("Usuario o contraseña incorrectos");
}

} else {
die("false");
}
?>

<?php session_start();
class ConnectionAdminArchivos {
protected $server = "localhost";
protected $user = "user";
protected $passwd = "kabongo696";
protected $db = "adminArchivost";
protected $dbCon;

function __construct() {
    $this->dbCon = mysqli_connect($this->server, $this->user, $this->passwd, $this->db);
    $this->dbCon->set_charset("utf8");
}

function __destruct() {
    mysqli_close($this->dbCon);
}

function getUsuario($email, $pass) {
    $query = "SELECT * FROM usuario WHERE correo = '$email' AND password = '$pass' LIMIT 1";
    $result = mysqli_query($this->dbCon, $query);
    $object = mysqli_fetch_object($result);
    return $object;
}
}
  ?>