Self hosted Dynamic DNS server using PHP and BIND

//
// Do any local configuration here
//

// Consider adding the 1918 zones here, if they are not used in your
// organization
//include "/etc/bind/zones.rfc1918";

zone "dns.example.com" IN {
    type master;
    file "/var/lib/bind/dns.example.com.zone";
    allow-update { ::1; 127.0.0.1;};
    notify no;
};

options {
	directory "/var/cache/bind";

	// If there is a firewall between you and nameservers you want
	// to talk to, you may need to fix the firewall to allow multiple
	// ports to talk.  See http://www.kb.cert.org/vuls/id/800113

	// If your ISP provided one or more IP addresses for stable
	// nameservers, you probably want to use them as forwarders.
	// Uncomment the following block, and insert the addresses replacing
	// the all-0's placeholder.

	// forwarders {
	// 	0.0.0.0;
	// };

	//========================================================================
	// If BIND logs error messages about the root key being expired,
	// you will need to update your keys.  See https://www.isc.org/bind-keys
	//========================================================================
	dnssec-validation auto;
	allow-transfer {none;};
	allow-notify {none;};
	allow-recursion {none;};
	allow-query-cache {none;};
	recursion no;
	minimal-any yes;
	minimal-responses yes;

	listen-on { 127.0.0.1; };
	listen-on-v6 { ::1; };
};

$ORIGIN .
$TTL 0	; 0 minutes
dns.example.com IN SOA dns.example.com. email.example.com. (
				100        ; serial
				3600       ; refresh (1 hour)
				3600       ; retry (1 hour)
				3600       ; expire (1 hour)
				0          ; minimum (0 seconds)
				)
$TTL 900	; 15 minutes
		IN	NS	dns.example.com.
; IP records for name servers
dns.example.com.             IN      AAAA       2001:0db8:a55b:42df:5d01:2359:a67e:737d
dns.example.com.             IN      A          203.0.113.9

<?php
header('Content-Type: text/plain');

$hostname = $_GET['hostname'] ?? null;
$ipV4Address = $_GET['myip'] ?? null;
$ipV6Address = $_GET['myipv6'] ?? null;
$dnsKey = $_GET['password'] ?? null;
$action = $_GET['action'] ?? null;
// DNS Time to live in seconds
$dnsttl = $_GET['ttl'] ?? '300';

if (isset($dnsKey) && preg_match('/[^a-zA-Z0-9]/', $dnsKey))
{
	echo 'badauth';
	exit;
}

if (isset($hostname) && preg_match('/[^a-z0-9\.\-\_]/', $hostname))
{
	echo 'notfqdn';
	exit;
}

if (isset($ipV4Address) && preg_match('/[^0-9\.]/', $ipV4Address))
{
	echo 'badsys';
	exit;
}

if (isset($ipV6Address) && preg_match('/[^a-f0-9\:]/', $ipV6Address))
{
	echo 'badsys';
	exit;
}

// Credintials format: hostname (homevpn.dns.example.com), password (rUOrbg8R2RvVmOhcVoOGnIRIgWCY0W5x), name of DNS zone to update (dns.example.com)
$login = false;
$user_info=[
'homevpn.dns.example.com'=>['rUOrbg8R2RvVmOhcVoOGnIRIgWCY0W5x','dns.example.com'],
'plexserver.dns.example.com'=>['vxV4uh77QhKlUZV7woenHogCGTZbENBf','dns.example.com'],
'fileserver.dns.example.com'=>['kYwi06FqLXDI77IJpZtM9N8VqiALymPR','dns.example.com'],
'gameserver.dns.example.com'=>['53o8DkXYCDB54mcL5l5x5C8OVPk8XRXM','dns.example.com']
];
foreach ($user_info as $key => $value) {
	$login = ($key == $hostname && $value[0] == $dnsKey) ? true : false;
	if($login) break;
}
if(!$login) {
	echo 'badauth';
	exit;
}

if ($hostname == null) {
	header('HTTP/1.1 400 Bad Request');
	echo 'notfqdn';
	exit;
}

if ($action == 'delete') {
$descriptorspec = array(
	0 => array('pipe', 'r'),
	1 => array('pipe', 'w')
);
$process = proc_open('nsupdate', $descriptorspec, $pipes, NULL, NULL);
fwrite($pipes[0], "server 127.0.0.1\n");
fwrite($pipes[0], "zone $value[1]\n");
fwrite($pipes[0], "update delete $hostname.\n");
fwrite($pipes[0], "send\n");
fclose($pipes[0]);
echo stream_get_contents($pipes[1]);
proc_close($process);
echo 'good';
exit;
}

if (!$ipV4Address and !$ipV6Address) {
$ip = $_SERVER['REMOTE_ADDR'];
if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4)) {
// Use client IP address if no IPv4 given
$ipV4Address = $ip;
} elseif (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6)) {
// Use client IP address if no IPv6 given
$ipV6Address = $ip;
}
}

// Check whether the given IPv4 address is valid
if ($ipV4Address and !filter_var($ipV4Address, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4)) {
	header('HTTP/1.1 400 Bad Request');
	echo 'badsys';
	exit;
}

// Check whether the given IPv6 address is valid
if ($ipV6Address and !filter_var($ipV6Address, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6)) {
	header('HTTP/1.1 400 Bad Request');
	echo 'badsys';
	exit;
}


if ($ipV4Address && $ipV6Address) {
	ipv4_update();
	ipv6_update();
}
elseif ($ipV6Address && !$ipV4Address) {
	ipv6_update();
	$descriptorspec = array(
		0 => array('pipe', 'r'),
							1 => array('pipe', 'w')
	);
	$process = proc_open('nsupdate', $descriptorspec, $pipes, NULL, NULL);
	fwrite($pipes[0], "server ::1\n");
	fwrite($pipes[0], "zone $value[1]\n");
	fwrite($pipes[0], "update delete $hostname. A\n");
	fwrite($pipes[0], "send\n");
	fclose($pipes[0]);
	echo stream_get_contents($pipes[1]);
	proc_close($process);
}
elseif ($ipV4Address && !$ipV6Address) {
	ipv4_update();
	$descriptorspec = array(
		0 => array('pipe', 'r'),
							1 => array('pipe', 'w')
	);
	$process = proc_open('nsupdate', $descriptorspec, $pipes, NULL, NULL);
	fwrite($pipes[0], "server ::1\n");
	fwrite($pipes[0], "zone $value[1]\n");
	fwrite($pipes[0], "update delete $hostname. AAAA\n");
	fwrite($pipes[0], "send\n");
	fclose($pipes[0]);
	echo stream_get_contents($pipes[1]);
	proc_close($process);
}

function ipv4_update()
{
global $hostname, $ipV4Address, $dnsttl, $value;
$descriptorspec = array(
	0 => array('pipe', 'r'),
	1 => array('pipe', 'w')
);
$process = proc_open('nsupdate', $descriptorspec, $pipes, NULL, NULL);
fwrite($pipes[0], "server 127.0.0.1\n");
fwrite($pipes[0], "zone $value[1]\n");
fwrite($pipes[0], "update delete $hostname. A\n");
fwrite($pipes[0], "update add $hostname. $dnsttl A $ipV4Address\n\n");
fclose($pipes[0]);
echo stream_get_contents($pipes[1]);
proc_close($process);
}

function ipv6_update()
{
global $hostname, $ipV6Address, $dnsttl, $value;
$descriptorspec = array(
	0 => array('pipe', 'r'),
	1 => array('pipe', 'w')
);
$process = proc_open('nsupdate', $descriptorspec, $pipes, NULL, NULL);
fwrite($pipes[0], "server 127.0.0.1\n");
fwrite($pipes[0], "zone $value[1]\n");
fwrite($pipes[0], "update delete $hostname. AAAA\n");
fwrite($pipes[0], "update add $hostname. $dnsttl AAAA $ipV6Address\n\n");
fclose($pipes[0]);
echo stream_get_contents($pipes[1]);
proc_close($process);
}

echo 'good';
?>