function Authenticate(username, password) {

    $.ajax({

            type: 'post',
            dataType: 'json',
            url: 'http://localhost/app/login.php',
            data: { action: 'auth', username: username, password: password },

            success: function(data){

                if(data.result == 'true') {

                    $(':mobile-pagecontainer').pagecontainer('change', '#events', {

                        transition: 'none',
                        changeHash: false,
                        reverse: false,
                        showLoadMsg: true

                    });

                }

                else {

                    $('#login-error').show();
                    $('#login-error').html('Usuário ou senha incorreta.');
                    $('#login-password').addClass('error');

                }


            },

            error: function() {

                alert('Erro Ajax');

            }

    });

}

case 'auth':

        $sql = "SELECT * FROM users WHERE username = ? AND password = ?";

        $username = $_POST['username'];
        $password = sha1($_POST['password']);

        $stmt = $conn->prepare($sql);
        $stmt->bind_param("ss", $username, $password);
        $stmt->execute();

        $result = $stmt->get_result();

        if($result->num_rows > 0) {

            $res = 'true';

        }

        else {

            $res = 'false';

        }

        echo json_encode(array("result" => $res));

        break;

case 'auth':

    $sql = "SELECT * FROM users WHERE username = ? AND password = ?";

    $username = $_POST['username'];
    $password = sha1($_POST['password']);

    $stmt = $conn->prepare($sql);
    $stmt->bind_param("ss", $username, $password);
    $stmt->execute();

    $result = $stmt->get_result();

    if($result->num_rows > 0) {

        session_start();
        $res = 'true';

    }

    else {

        $res = 'false';

    }

    echo json_encode(array("result" => $res, "sessid" => session_id()));

    break;

if( isset($_POST['sess_id']) ){
     session_id($_POST['sess_id']);
     session_start();
 }else {
    /**
     caso não tenha sido enviado um post contendo um id de sessão
     redirecionar para ua página de erro!
     */
 }