* rewrite the hole script:

** use .env file for config so we can retrieve updates
** add config and payload DTO with validators
** allow registrable domains as DynDNS
** update IPv4/6 only if changed (or really forced)
** remove obsolete failed_logins counter
** save logs with timestamp
** save only the newest 100 log entries for each domain

src/Payload.php

@@ -0,0 +1,156 @@
+<?php
+
+namespace netcup\DNS\API;
+
+final class Payload
+{
+    /**
+     * @var string
+     */
+    private $user;
+
+    /**
+     * @var string
+     */
+    private $password;
+
+    /**
+     * @var string
+     */
+    private $domain;
+
+    /**
+     * @var string
+     */
+    private $ipv4;
+
+    /**
+     * @var string
+     */
+    private $ipv6;
+
+    /**
+     * @var bool
+     */
+    private $force = false;
+
+    public function __construct(array $payload)
+    {
+        foreach (get_object_vars($this) as $key => $val) {
+            if (isset($payload[$key])) {
+                $this->$key = $payload[$key];
+            }
+        }
+    }
+
+    /**
+     * @return bool
+     */
+    public function isValid()
+    {
+        return
+            !empty($this->user) &&
+            !empty($this->password) &&
+            !empty($this->domain) &&
+            (
+                (
+                    !empty($this->ipv4) && $this->isValidIpv4()
+                )
+                ||
+                (
+                    !empty($this->ipv6) && $this->isValidIpv6()
+                )
+            );
+    }
+
+    /**
+     * @return string
+     */
+    public function getUser()
+    {
+        return $this->user;
+    }
+
+    /**
+     * @return string
+     */
+    public function getPassword()
+    {
+        return $this->password;
+    }
+
+    /**
+     * @return string
+     */
+    public function getDomain()
+    {
+        return $this->domain;
+    }
+
+    /**
+     * there is no good way to get the correct "registrable" Domain without external libs!
+     *
+     * @see https://github.com/jeremykendall/php-domain-parser
+     *
+     * this method is still tricky, because:
+     *
+     * works: nas.tld.com
+     * works: nas.tld.de
+     * works: tld.com
+     * failed: nas.tld.co.uk
+     * failed: nas.home.tld.de
+     *
+     * @return string
+     */
+    public function getHostname()
+    {
+        // hack if top level domain are used for dynDNS
+        if (1 === substr_count($this->domain, '.')) {
+            return $this->domain;
+        }
+
+        $domainParts = explode('.', $this->domain);
+        array_shift($domainParts); // remove sub domain
+        return implode('.', $domainParts);
+    }
+
+    /**
+     * @return string
+     */
+    public function getIpv4()
+    {
+        return $this->ipv4;
+    }
+
+    /**
+     * @return bool
+     */
+    public function isValidIpv4()
+    {
+        return (bool)filter_var($this->ipv4, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4);
+    }
+
+    /**
+     * @return string
+     */
+    public function getIpv6()
+    {
+        return $this->ipv6;
+    }
+
+    /**
+     * @return bool
+     */
+    public function isValidIpv6()
+    {
+        return (bool)filter_var($this->ipv6, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6);
+    }
+
+    /**
+     * @return bool
+     */
+    public function isForce()
+    {
+        return $this->force;
+    }
+}