disable-rest-api.php

<?php
defined('ABSPATH') or die();

/*
MU Plugin: disable-rest-api
Description: Disable rest api
Author: Yann Kozon
Author URI: https://www.yannkozon.com
*/

function mu_disable_rest_api() {
	if( ! is_user_logged_in() ) {
	    remove_action( 'init',          'rest_api_init' );
		remove_action( 'parse_request', 'rest_api_loaded' );

		remove_action( 'xmlrpc_rsd_apis',            'rest_output_rsd' );
		remove_action( 'wp_head',                    'rest_output_link_wp_head' );
		remove_action( 'template_redirect',          'rest_output_link_header', 11 );
		remove_action( 'auth_cookie_malformed',      'rest_cookie_collect_status' );
		remove_action( 'auth_cookie_expired',        'rest_cookie_collect_status' );
		remove_action( 'auth_cookie_bad_username',   'rest_cookie_collect_status' );
		remove_action( 'auth_cookie_bad_hash',       'rest_cookie_collect_status' );
		remove_action( 'auth_cookie_valid',          'rest_cookie_collect_status' );

		add_filter( 'rest_enabled',       '__return_false' );
		add_filter( 'rest_jsonp_enabled', '__return_false' );
	}
}

add_action( 'init', 'mu_disable_rest_api' );