Whitelists allowed redirect hosts for safe HTTP requests as well.

Attached to the http_request_host_is_external filter.

Signature

allowed_http_request_hosts( $is_external, $host )
is_external
 (boolean)
host
 (string)

Return

(boolean)

Source

function allowed_http_request_hosts( $is_external, $host ) {
	if ( ! $is_external && wp_validate_redirect( 'http://' . $host ) )
		$is_external = true;
	return $is_external;
}
WP Trac GitHub

Link here