Filter for allowing local theme and plugin repo updates (for testing, never us on production site)

allow-my-custom-host.php

<?php
/** Enable my local themes and plugins repository FFS!!! */
function allow_my_custom_host( $allow, $host, $url ) {
  if ( $host == 'put-your-repository-domain-here.com' )
  	$allow = true;
  return $allow;
}
add_filter( 'http_request_host_is_external', 'allow_my_custom_host', 10, 3 );