WordPress REST API - Get Random Post endpoint

plugin.php

<?php

/**
 * Plugin Name: WP Slack REST API Backend
 * Description: An example of using the WordPress REST API as a backend for a Slack Bot
 * Author: Andy Brudtkuhl
 * Author URI: http://youmetandy.com
 * Version: 0.1
 * Plugin URI: https://github.com/abrudtkuhl/heykramer
 * License: GPL2+
 */

add_action( 'rest_api_init', function () {
    register_rest_route( 'api', '/any', array(
        'methods'   =>  'GET',
        'callback'  =>  'get_random',
    ) );
}

function get_random() {
    return get_posts( array( 'orderby' => 'rand', 'posts_per_page' => 1) );
}

Add orderby => rand to existing posts api endpoint:

function my_rest_post_collection_params($query_params) {
	$query_params['orderby']['enum'][] = 'rand';
	return $query_params;
}
add_filter('rest_post_collection_params', 'my_rest_post_collection_params');

Now this works:
/wp-json/wp/v2/posts?orderby=rand

rest_{post_type}_collection_params