diff --git a/classes/class.xoctSecureLink.php b/classes/class.xoctSecureLink.php
index b28c7ce2..d25f0bf2 100644
--- a/classes/class.xoctSecureLink.php
+++ b/classes/class.xoctSecureLink.php
@@ -20,24 +20,16 @@ class xoctSecureLink
     protected static $cache = [];
 
     /**
-     * @param       $url
-     *
-     * @param null  $valid_until
-     *
-     * @param false $restict_ip
-     *
-     * @return mixed
-     * @throws xoctException
      * @deperecated we should get rid of static methods
      */
-    protected static function sign($url, $valid_until = null, $restict_ip = false)
+    protected static function sign(string $url, ?string $valid_until = null, ?bool $restict_ip = false)
     {
         $opencastContainer = Init::init();
         if (str_contains((string) $url, 'policy=') && str_contains((string) $url, 'signature=')) {
             // already signed, e.g. when presigning is active
             return $url;
         }
-        if (!$url) {
+        if ($url === '' || $url === '0') {
             return '';
         }
         if (isset(self::$cache[$url])) {
@@ -46,56 +38,38 @@ protected static function sign($url, $valid_until = null, $restict_ip = false)
 
         $ip = ($restict_ip) ? self::getClientIP() : null;
 
-        $data = $opencastContainer[API::class]->routes()->securityApi->sign($url, $valid_until, $ip);
+        $data = $opencastContainer[API::class]->routes()->securityApi->sign($url, $valid_until ?? '', $ip);
 
-        if ($data->error) {
+        if ($data->error ?? false) {
             // We would only be able to log it here as error to avoid further confilicts.
             xoctLog::getInstance()->write(
                 "[Error]: Signing link ($url) failed: {$data->error}",
                 xoctLog::DEBUG_LEVEL_1
             );
-            return '';
+            return $url;
         }
         self::$cache[$url] = $data->url;
 
         return $data->url;
     }
 
-    /**
-     * @param $url
-     *
-     * @return mixed
-     * @throws xoctException
-     */
-    public static function signThumbnail($url)
+
+    public static function signThumbnail(string $url): string
     {
         $duration = PluginConfig::getConfig(PluginConfig::F_SIGN_THUMBNAIL_LINKS_TIME);
         $valid_until = ($duration > 0) ? gmdate("Y-m-d\TH:i:s\Z", time() + $duration) : null;
         return self::sign($url, $valid_until, PluginConfig::getConfig(PluginConfig::F_SIGN_THUMBNAIL_LINKS_WITH_IP));
     }
 
-    /**
-     * @param $url
-     *
-     * @return mixed
-     * @throws xoctException
-     */
-    public static function signAnnotation($url)
+
+    public static function signAnnotation(string $url): string
     {
         $duration = PluginConfig::getConfig(PluginConfig::F_SIGN_ANNOTATION_LINKS_TIME);
         $valid_until = ($duration > 0) ? gmdate("Y-m-d\TH:i:s\Z", time() + $duration) : null;
         return self::sign($url, $valid_until, PluginConfig::getConfig(PluginConfig::F_SIGN_ANNOTATION_LINKS_WITH_IP));
     }
 
-    /**
-     * @param   $url
-     *
-     * @param 0 $duration
-     *
-     * @return mixed
-     * @throws xoctException
-     */
-    public static function signPlayer($url, $duration = 0)
+    public static function signPlayer(string $url, int $duration = 0): string
     {
         $valid_until = null;
         if (PluginConfig::getConfig(PluginConfig::F_SIGN_PLAYER_LINKS_OVERWRITE_DEFAULT) && $duration > 0) {
@@ -103,9 +77,10 @@ public static function signPlayer($url, $duration = 0)
             $additional_time_percent = PluginConfig::getConfig(
                 PluginConfig::F_SIGN_PLAYER_LINKS_ADDITIONAL_TIME_PERCENT
             ) / 100;
+            $calculated_timestamp = time() + $duration_in_seconds + $duration_in_seconds * $additional_time_percent;
             $valid_until = gmdate(
                 "Y-m-d\TH:i:s\Z",
-                time() + $duration_in_seconds + $duration_in_seconds * $additional_time_percent
+                (int) $calculated_timestamp
             );
         }
         $url_path = parse_url((string) $url, PHP_URL_PATH);
@@ -113,43 +88,39 @@ public static function signPlayer($url, $duration = 0)
         if ($extension === 'mp4' && !PluginConfig::getConfig(PluginConfig::F_SIGN_PLAYER_LINKS_MP4)) {
             return $url;
         }
-        return self::sign($url, $valid_until, PluginConfig::getConfig(PluginConfig::F_SIGN_PLAYER_LINKS_WITH_IP));
+        return self::sign(
+            $url,
+            $valid_until,
+            (bool) PluginConfig::getConfig(PluginConfig::F_SIGN_PLAYER_LINKS_WITH_IP)
+        );
     }
 
-    /**
-     * @param $url
-     *
-     * @return mixed
-     * @throws xoctException
-     */
-    public static function signDownload($url)
+    public static function signDownload(string $url): string
     {
         $duration = PluginConfig::getConfig(PluginConfig::F_SIGN_DOWNLOAD_LINKS_TIME);
-        $valid_until = ($duration > 0) ? gmdate("Y-m-d\TH:i:s\Z", time() + $duration) : null;
+        $valid_until = ($duration > 0) ? gmdate("Y-m-d\TH:i:s\Z", (int) (time() + $duration)) : null;
+
         return self::sign($url, $valid_until);
     }
 
-    /**
-     * @return mixed|string
-     */
     protected static function getClientIP(): string
     {
-        if ($_SERVER['HTTP_CLIENT_IP']) {
+        if ($_SERVER['HTTP_CLIENT_IP'] ?? null) {
             return $_SERVER['HTTP_CLIENT_IP'];
         }
-        if ($_SERVER['HTTP_X_FORWARDED_FOR']) {
+        if ($_SERVER['HTTP_X_FORWARDED_FOR'] ?? null) {
             return $_SERVER['HTTP_X_FORWARDED_FOR'];
         }
-        if ($_SERVER['HTTP_X_FORWARDED']) {
+        if ($_SERVER['HTTP_X_FORWARDED'] ?? null) {
             return $_SERVER['HTTP_X_FORWARDED'];
         }
-        if ($_SERVER['HTTP_FORWARDED_FOR']) {
+        if ($_SERVER['HTTP_FORWARDED_FOR'] ?? null) {
             return $_SERVER['HTTP_FORWARDED_FOR'];
         }
-        if ($_SERVER['HTTP_FORWARDED']) {
+        if ($_SERVER['HTTP_FORWARDED'] ?? null) {
             return $_SERVER['HTTP_FORWARDED'];
         }
-        if ($_SERVER['REMOTE_ADDR']) {
+        if ($_SERVER['REMOTE_ADDR'] ?? null) {
             return $_SERVER['REMOTE_ADDR'];
         }
         return '';