Wordpress - How to login user to frontend programmatically - wordpress

Question

I created function for loging in users on frontend using this example: https://gist.github.com/iandunn/8162246
After user logs in is_user_logged_in() function returns true only inside this function where I placed code for login part.
How do I login users globally?
This is my code:
function programmatic_login( $username ) {
if ( is_user_logged_in() ) {
wp_logout();
}
add_filter( 'authenticate', 'allow_programmatic_login', 10, 3 );
$user = wp_signon( array( 'user_login' => $username ) );
remove_filter( 'authenticate', 'allow_programmatic_login', 10, 3 );
if ( is_a( $user, 'WP_User' ) ) {
$user_id = $user->ID;
if( $user ) {
wp_set_current_user( $user_id, $user->user_login );
wp_set_auth_cookie( $user_id );
do_action( 'wp_login', $user->user_login );
}
if ( is_user_logged_in() ) {
return true;
}
}
return false;
}
function allow_programmatic_login( $user, $username, $password ) {
return get_user_by( 'login', $username );
}
function process_login(){
// this comes from login form
$username = $_POST["login_username"];
programmatic_login( $username );
// it returns true only here, on any other function it returns false
if(is_user_logged_in()){
echo "ok";
}else{
echo "not ok";
}
}
This is one example where I try to check if user is logged in, outside previous function:
add_filter('wp_nav_menu_items', 'add_login_logout_link', 10, 2);
function add_login_logout_link($items, $args) {
$loginPage = get_page_by_title("Login");
$registerPage = get_page_by_title("Register");
if(is_user_logged_in()){
$items .= "<li><a href='" . wp_logout_url('index.php') . "' title='Logout'>Logout</a></li>";
}else{
$items .= "<li><a href='". site_url() . '/' . '?page_id=' . $loginPage->ID ."'>Login</a></li><li><a a href='". site_url() . '/' . '?page_id=' . $registerPage->ID ."'>Register</a></li>";
}
return $items;
}

Answer 1

On codex wp_set_current_user there is an example to set the current user and log them in.
$user_id = 12345;
$user = get_user_by( 'id', $user_id );
if( $user ) {
wp_set_current_user( $user_id, $user->user_login );
wp_set_auth_cookie( $user_id );
do_action( 'wp_login', $user->user_login );
}

Answer 2

The simplest fix is to use wp_login_form()
see reference: http://codex.wordpress.org/Function_Reference/wp_login_form
If i understand correctly this should handle everything you want.
This will set the auth cookie and can redirect to the page you want, the login works globally