diff --git a/common/account_utils.php b/common/account_utils.php
index 884d8da..8ee181f 100644
--- a/common/account_utils.php
+++ b/common/account_utils.php
@@ -72,3 +72,15 @@ function get_user_display_name($userId, $escape = true) {
 
     return $display_name;
 }
+
+function requires_auth($redirect = '/auth/login') {
+    global $path_raw;
+
+    if ($_SESSION['auth']) {
+        return true;
+    }
+
+    http_response_code(307);
+    header('Location: '.$redirect.'?callback='.urlencode($path_raw));
+    exit();
+}
diff --git a/common/strings.php b/common/strings.php
index 618ad18..93333e7 100644
--- a/common/strings.php
+++ b/common/strings.php
@@ -1,6 +1,6 @@
 <?php
 
-function get_string($key="generic.generic") {
+function get_string($key="generic.generic", $substitutes=[]) {
     global $LANG;
 
     $key_path = explode('.', $key);
@@ -15,10 +15,20 @@ function get_string($key="generic.generic") {
         }
     }
 
+    if (count($substitutes) > 0) {
+        foreach ($substitutes as $key => $substitute) {
+            $re = '/{{('. $key .')}}/';
+            $subst = $substitute;
+
+            $result = preg_replace($re, $subst, $result, 1);
+        }
+    }
+
     return $result;
 }
 
-function patch_lang($lang="en") {
+function patch_lang($lang="en"): void
+{
 
     global $LANG, $DOC_ROOT;