page-register.php

<?php
/**
 * Template Name: Registration Page
 *
 * This is the template that displays all pages by default.
 * Please note that this is the WordPress construct of pages
 * and that other 'pages' on your WordPress site may use a
 * different template.
 *
 * @link https://developer.wordpress.org/themes/basics/template-hierarchy/
 *
 * @package worldofdominas
 */


 if ( isset($_POST['submit'] ) ) {
    $username = sanitize_text_field( $_POST['username'] );
    $email = sanitize_email( $_POST['email'] );
    $password = sanitize_text_field( $_POST['password'] );

    $errors = array();

    if ( empty( $username ) || empty( $email ) || empty( $password ) ) {
        $errors[] = 'Пожалуйста, заполните все обязательные поля.';
    }

    if ( !is_email( $email ) ) {
        $errors[] = 'Неверный формат email.';
    }

    if ( username_exists( $username ) ) {
        $errors[] = 'Логин уже занят.';
    }

    if ( email_exists( $email ) ) {
        $errors[] = 'Email уже зарегистрирован.';
    }

    if ( empty( $errors ) ) {
        wp_create_user( $username, $password, $email );
        echo '<div style="color: green;">Регистрация прошла успешно!</div>';
    } else {
        foreach ( $errors as $error ) {
            echo '<div style="color: red;">' . $error . '</div>';
        }
    }
}


get_header();
?>

    <main id="primary">

    <div class="registration-form">
    <form action="<?php echo esc_url( $_SERVER['REQUEST_URI'] ); ?>" method="post">
        <p>
            <label for="username">Логин <strong>*</strong></label>
            <input type="text" name="username" value="<?php echo ( isset( $_POST['username'] ) ? esc_attr( $_POST['username'] ) : '' ); ?>" size="40" />
        </p>
        <p>
            <label for="email">Email <strong>*</strong></label>
            <input type="email" name="email" value="<?php echo ( isset( $_POST['email'] ) ? esc_attr( $_POST['email'] ) : '' ); ?>" size="40" />
        </p>
        <p>
            <label for="password">Пароль <strong>*</strong></label>
            <input type="password" name="password" value="<?php echo ( isset( $_POST['password'] ) ? esc_attr( $_POST['password'] ) : '' ); ?>" size="40" />
        </p>
        <p>
            <input type="submit" name="submit" value="Регистрация"/>
        </p>
    </form>
</div>

    </main><!-- #main -->

<?php get_footer();?>