WordPress│WP REST APIとGASを使った投稿・更新方法

function wazaRequest(path, method, payload) {
  const p = PropertiesService.getScriptProperties();
  const base = (p.getProperty('WP_SITE_URL') || '').replace(/\/+$/, '');
  const user = p.getProperty('WP_USER');
  const pass = p.getProperty('WP_APP_PASSWORD');
  if (!/^https:\/\/[^\s/?#@:]+(?:\/[^\s?#]*)?$/.test(base) || !user || !pass) {
    throw new Error('HTTPSのサイトURLと認証用プロパティを確認してください');
  }
  if (!/^\/posts(?:\/[1-9]\d*)?(?:\?context=edit)?$/.test(path)) throw new Error('対象パスが不正です');
  const options = {
    method: method, contentType: 'application/json',
    headers: {Authorization: 'Basic ' + Utilities.base64Encode(user + ':' + pass)},
    muteHttpExceptions: true, followRedirects: false
  };
  if (payload !== undefined) options.payload = JSON.stringify(payload);
  const response = UrlFetchApp.fetch(base + '/wp-json/wp/v2' + path, options);
  const status = response.getResponseCode();
  if (status < 200 || status >= 300) throw new Error('WordPress HTTP ' + status);
  return JSON.parse(response.getContentText());
}
function wazaCreateDraft() {
  const post = wazaRequest('/posts', 'post', {
    title: '自動投稿テスト', content: '<p>下書きのテストです。</p>', status: 'draft'
  });
  return post.id; // IDを控える。再実行すると別の下書きが作られる。
}
function wazaReadPost(postId) {
  if (!Number.isSafeInteger(postId) || postId <= 0) throw new Error('投稿IDが不正です');
  return wazaRequest('/posts/' + postId + '?context=edit', 'get');
}
function wazaUpdatePost(postId, expectedModified, title, content) {
  const current = wazaReadPost(postId);
  if (!expectedModified || current.modified_gmt !== expectedModified) throw new Error('更新競合: 最新版を確認してください');
  return wazaRequest('/posts/' + postId, 'post', {title: title, content: content});
}
function wazaUpdateNote(postId, text) {
  if (!Number.isSafeInteger(postId) || postId <= 0 || typeof text !== 'string') throw new Error('入力が不正です');
  return wazaRequest('/posts/' + postId, 'post', {meta: {waza_note: text}});
}

function waza_register_note_meta() {
    register_post_meta('post', 'waza_note', array(
        'type' => 'string',
        'single' => true,
        'sanitize_callback' => 'sanitize_text_field',
        'auth_callback' => function ($allowed, $key, $post_id) {
            return current_user_can('edit_post', $post_id);
        },
        'show_in_rest' => array('schema' => array(
            'type' => 'string', 'context' => array('edit'),
        )),
    ));
}
add_action('init', 'waza_register_note_meta');