Verification of CNAME record for custom domain

When we give users option to connect their own domain to our service, we must also check that the DNS record has the correct CNAME settings before we approve such a domain.

We can use a simple helper that will do the verification:

/**
 * Verify CNAME for domain
 *
 * @param string $host
 *
 * @return bool
 */
function verifyCname(string $host): bool
{
    $result  = false;
    $records = dns_get_record($host, DNS_CNAME);

    foreach ($records as $row) {
        if ($row['type'] === 'CNAME') {
            if ($row['host'] === $host && $row['target'] === 'add your valid cname record value here') {
                $result = true;
            } else {
                return false;
            }
        }
    }

    return $result;
}

It would be good to verify beforehand that the hostname given by the user is correct, or at least has a chance to be correct. For this purpose, we can use the list of available domains:

https://github.com/incognico/list-of-top-level-domains

With the right choice of verification, we will be able to weed out domains that are clearly not valid or simply cannot exist.