always-login.php

<?php

/**
 * keeps a user always logged in
 * don't use this on a production site, ever!
 */

add_action('init', 'auto_login');
add_action('admin_init', 'auto_login');
function auto_login() {
	if (!is_user_logged_in()) {
		$user = get_userdata(1); // 1 being the ID that I want

		wp_set_current_user($user->ID, $user->user_login);
		wp_set_auth_cookie($user->ID);
		do_action('wp_login', $user->user_login);
	}
}