Simple WordPress plugin to require login for site access, showing welcome content on frontpage for non-authenticated users. Uses personalized links to authorize access to feeds.

wp_require_login.php

<?php
/*
Plugin Name: Require Login
Plugin URI:
Author: Goran Rakic
Version: 2.0
Author URI: http://blog.goranrakic.com
*/

/**
 * If user is not logged in display a static welcome page.
 * Allow access to feeds if feedkey is provided.
 * Else redirect to login page.
 */
function require_login_redirect()
{
    if (!is_user_logged_in()) {
        if (is_front_page()) {
            /* FIXME: Show welcome page
            Load custom welcome page here (can be set with options api)
            or include any other static content...
            */
            require(ABSPATH . '/static.php');
            exit;
        } elseif (is_feed() && isset($_GET['feedkey']) && feedkey_check($_GET['feedkey'])) {
            return;      // do not redirect for feeds if feedkey is valid
        }
        auth_redirect(); // redirect if not logged in
    }
}
add_action('template_redirect', 'require_login_redirect', 1);

/**
 * Add feedkey to all feed links
 */
function require_login_add_feedkey($url)
{
    $uid = get_current_user_id();
    return add_query_arg(array('feedkey' => feedkey_gen($uid)), $url);
}
add_filter('feed_link', 'require_login_add_feedkey');
add_filter('post_comments_feed_link', 'require_login_add_feedkey');
add_filter('category_feed_link', 'require_login_add_feedkey');
add_filter('author_feed_link', 'require_login_add_feedkey');
add_filter('tag_feed_link', 'require_login_add_feedkey');
add_filter('search_feed_link', 'require_login_add_feedkey');

// FIXME: Use password_hash/password_verify for PHP>=5.5
function feedkey_gen($uid)
{
    return $uid . '-' . md5(wp_salt('auth') . $uid);
}
function feedkey_check($feedkey)
{
    $uid = substr($feedkey, 0, strpos($feedkey, '-'));
    return feedkey_gen($uid) === $feedkey;
}

/**
 * By default redirect to homepage after login
 */
function require_login_admin_default_page($redirect_to, $request, $user)
{
    if (isset($_GET['redirect_to']))
        return $_GET['redirect_to'];

    if ($redirect_to == admin_url())
        return home_url();

    return $redirect_to;
}
add_filter('login_redirect', 'require_login_admin_default_page');