Make annoying WordPress plugins that constantly perform license checks in the admin behave.

cache-aggressive-license-checks.php

<?php
/**
 * Plugin Name: Cache Aggressive License Checks
 * Description: Cache the license checks for plugins that are lame and check on every request.
 * Author: Doug Cone
 * Author URI: http://dougcone.com
 * Version: 0.0.1
 *
 */

namespace nullvariable;

add_filter( 'pre_http_request', [ '\nullvariable\Cache_License_Checks', 'pre_http_request' ], 1, 3 );
add_filter( 'http_response', [ '\nullvariable\Cache_License_Checks', 'http_response' ], 1, 3 );
/**
 * Cache_License_Checks class
 */
class Cache_License_Checks {
	/**
	 * Domains to cache.
	 *
	 * @var $domains_to_cache array domains strings.
	 */
	public static $domains_to_cache = [
		'example.com',
		'www.anotherslowapidomain.com',
	];

	/**
	 * Pre_http_request filter for http class.
	 *
	 * Returns cache, if we have it.
	 *
	 * @param false|array|WP_Error $preempt Filtered content.
	 * @param array                $args Request args.
	 * @param string               $url Request url.
	 * @return false|array
	 */
	public static function pre_http_request( $preempt, $args, $url ) {
		$domain = wp_parse_url( $url, PHP_URL_HOST );
		if ( in_array( $domain, self::$domains_to_cache, true ) ) {
			$preempt = wp_cache_get( md5( $url ), 'nv_license_cache' );
		}
		return $preempt;
	}

	/**
	 * Http_response filter for http class.
	 *
	 * Sets a cache value for requests we wish to cache.
	 *
	 * @param array  $response HTTP response array.
	 * @param array  $args HTTP request arguments.
	 * @param string $url The request URL.
	 * @return array Response array.
	 */
	public static function http_response( $response, $args, $url ) {
		$domain = wp_parse_url( $url, PHP_URL_HOST );
		if ( in_array( $domain, self::$domains_to_cache, true ) ) {
			wp_cache_set( md5( $url ), $response, 'nv_license_cache', DAY_IN_SECONDS );
		}
		return $response;
	}
}

I use New Relic to find these bad actors, and then just add them to the array on Line 24.