PHP function to get number of days before SSL/TLS certificate expiry from a HTTPS URL

get_ssl_expiry.php

<?php

/**
 * Return number of days before certificate expiry from a HTTPS URL
 * Usage: get_ssl_certificate_expiry('https://www.framasoft.net/')
 * => int(45)
 * @author bohwaz
 */
function get_ssl_certificate_expiry(string $url): ?int
{
	$url = parse_url($url);

	if ($url['scheme'] != 'https') {
		return null;
	}

	$get = stream_context_create(array("ssl" => array("capture_peer_cert" => TRUE)));
	$read = stream_socket_client(sprintf("ssl://%s:443", $url['host']), $errno, $errstr, 5, STREAM_CLIENT_CONNECT, $get);
	$cert = stream_context_get_params($read);

	if (!isset($cert['options']['ssl']['peer_certificate'])) {
		return 0;
	}

	$certinfo = openssl_x509_parse($cert['options']['ssl']['peer_certificate']);
	$date = $certinfo['validTo_time_t'] ?? null;

	if (!$date) {
		return 0;
	}

	return intval(($date - time()) / 3600 / 24);
}