Activate REST API for WordPress.

enable-rest-comment.php

<?php
/*
Plugin Name:  Activate REST API
Plugin URI:   https://wordpress.org/plugins/enable-anonymous-rest-comment/
Description:  Enable comments via rest api without login. Give front-end raw HTML via REST API.
Version:      0.2
Author:       Cooler
Author URI:   https://gist.github.com/rikakomoe/ec905d5378fbfbdd585ab63dfd39c609
License:      Unlicense
License URI:  https://unlicense.org/
*/

add_filter( 'rest_allow_anonymous_comments', '__return_true' );
add_action( 'rest_api_init', function () {
   register_rest_field(
          'page',
          'content',
          array(
                 'get_callback'    => 'compasshb_do_shortcodes',
                 'update_callback' => null,
                 'schema'          => null,
          )
       );
});
function compasshb_do_shortcodes( $object, $field_name, $request ) {
   WPBMap::addAllMappedShortcodes(); // This does all the work
   global $post;
   $post = get_post ($object['id']);
   $output['rendered'] = apply_filters( 'the_content', $post->post_content );
   return $output;
}