diff --git a/php/auth.php b/php/auth.php
index 1447296f..93ab86fc 100644
--- a/php/auth.php
+++ b/php/auth.php
@@ -1,4 +1,5 @@
 <?php
+require('func.php');
 $ERRORLOG = getenv('PHP_ERROR_LOG');
 if (empty($ERRORLOG)) {
     $ERRORLOG = '/var/log/lighttpd/error.log';
@@ -49,4 +50,11 @@ if(!isset($_SESSION['token'], $_POST['token']) || !hash_equals($_SESSION['token'
     log_and_die("Wrong token");
 }
 
+if(isset($_POST['domain'])){
+    $validDomain = is_valid_domain_name($_POST['domain']);
+    if(!$validDomain){
+        log_and_die($_POST['domain']. ' is not a valid domain');
+    }
+}
+
 ?>
diff --git a/php/func.php b/php/func.php
new file mode 100644
index 00000000..060b4f43
--- /dev/null
+++ b/php/func.php
@@ -0,0 +1,10 @@
+<?php
+
+function is_valid_domain_name($domain_name)
+{
+    return (preg_match("/^([a-z\d](-*[a-z\d])*)(\.([a-z\d](-*[a-z\d])*))*$/i", $domain_name) &&  //valid chars check
+        preg_match("/^.{1,253}$/", $domain_name) && //overall length check
+        preg_match("/^[^\.]{1,63}(\.[^\.]{1,63})*$/", $domain_name)); //length of each label
+}
+
+?>
\ No newline at end of file