unsupervised-scheduler/src/Frontend/LoginPage.php

<?php
declare(strict_types=1);

namespace Unsupervised\Schedular\Frontend;

class LoginPage
{
    public function render(array $atts): string
    {
        if (is_user_logged_in()) {
            $redirect = esc_url(get_permalink());
            return sprintf(
                '<p>%s <a href="%s">%s</a>.</p>',
                esc_html__('You are already logged in.', 'unsupervised-schedular'),
                $redirect,
                esc_html__('View available lessons', 'unsupervised-schedular')
            );
        }

        $error    = '';
        $redirect = sanitize_url(get_permalink() ?? '');

        if (isset($_POST['us_login']) && check_admin_referer('us_student_login')) {
            $credentials = [
                'user_login'    => sanitize_user($_POST['log'] ?? ''),
                'user_password' => $_POST['pwd'] ?? '',
                'remember'      => isset($_POST['rememberme']),
            ];

            $user = wp_signon($credentials, false);

            if (is_wp_error($user)) {
                $error = esc_html__('Invalid username or password.', 'unsupervised-schedular');
            } else {
                wp_safe_redirect($redirect);
                exit;
            }
        }

        ob_start();
        include USC_PLUGIN_DIR . 'templates/frontend/login-page.php';
        return (string) ob_get_clean();
    }
}