BjornW

RESTless is a tiny WordPress plugin which disables access to the REST API (available in WordPress since version 4.4) for non-authenticated users. 
This prevents usage of the REST API by the general public and limits access to those with login credentials. No REST for the wicked.
It also supports WordPress Multisite installations.
<h3>Notes</h3>
Credits:
Sword icon used in the WordPress plugin repository and found as /assets/icon* 
From the series <a href="http://www.toicon.com/series/sketchy" rel="nofollow ugc">‘Sketchy’</a> By <a href="http://www.toicon.com/authors/1" rel="nofollow ugc">Shannon E Thomas</a>
Thanks Shannon E Thomas and to[icon] for sharing your work!
WordPress repository banner image found in /assets/banner*:
Orginal painting: <a href="http://hdl.handle.net/10934/RM0001.COLLECT.319230" rel="nofollow ugc">‘Draak’</a> 
Drawn by: <a href="https://en.wikipedia.org/wiki/Utagawa_Kuniyoshi" rel="nofollow ugc">Utagawa Kuniyoshi</a> 
Dated around 1808 – 1861 
Repository: Rijksmuseum.nl 
Modified by: <a href="https://burobjorn.nl" rel="nofollow ugc">Björn Wijers</a>
Thanks Rijksmuseum!

RESTless

RESTless disables REST calls for non-authenticated requests.

Andr&eacute; Boekhorst

This plugin combines the two of the best WordPress plugins: <a href="https://wordpress.org/plugins/advanced-custom-fields/" title="Advanced Custom Fields" rel="ugc">Advanced Custom Fields</a> and <a href="https://wordpress.org/plugins/json-rest-api/" title="WP REST API" rel="ugc">WP REST API</a>.
This plugin is based on the work from<a href="https://github.com/PanManAms/WP-JSON-API-ACF" title="Panman on Github" rel="nofollow ugc">Panman on Github</a>. He was right when he said it would be better as plugin, but it would be even better if it would be available through the WordPress Plugin Repository.
An addition made to this plugin is that each ACF Field van be filtered throug the hook: JSON_META_ACFFIELDNAME (where ACFFIELDNAME depends on the fieldname you’ve added in the Advanced Custom Fields backend.)

WP REST API Custom Fields

The plugin is installed but nothing is in the output of API

JUst does not work

Shows Advanced Custom Field output to the WP REST API for posts, pages, taxonomies and users.

RESTless vs WP REST API Custom Fields