// Add to your theme's functions.php or a custom plugin

/**
 * Capture the referring URL before user navigates to the login page.
 */
function wbcom_capture_referring_url() {
    // Check if the current page is the WordPress login page and the user is not logged in
    if ( strpos($_SERVER['REQUEST_URI'], 'wp-login.php') !== false && !is_user_logged_in() ) {
        // Get the referrer URL
        $referrer = wp_get_referer();
        // If there's a referrer, store it in a session variable
        if ( !empty($referrer) ) {
            $_SESSION['wbcom_login_referrer'] = $referrer;
        }
    }
}
add_action('wp', 'wbcom_capture_referring_url');

/**
 * Redirect user to the previously captured URL after successful login.
 */
function wbcom_redirect_after_login( $redirect_to, $requested_redirect_to, $user ) {
    // Check if our session variable with the referrer URL is set
    if ( isset($_SESSION['wbcom_login_referrer']) ) {
        // Store the URL
        $redirect_url = $_SESSION['wbcom_login_referrer'];
        // Unset the session variable for future logins
        unset($_SESSION['wbcom_login_referrer']);
        // Redirect to the stored URL
        return $redirect_url;
    }
    // If no referrer URL was captured, proceed with the default redirect
    return $redirect_to;
}
add_filter('login_redirect', 'wbcom_redirect_after_login', 10, 3);