change to using file for cache rather than session

Author: MartinLenord

src/lti/Cache.php

@@ -2,26 +2,45 @@
 namespace IMSGlobal\LTI;
 
 class Cache {
+
+    private $cache;
+
     public function get_launch_data($key) {
-        return $_SESSION[$key];
+        $this->load_cache();
+        return $this->cache[$key];
     }
 
     public function cache_launch_data($key, $jwt_body) {
-        $_SESSION[$key] = $jwt_body;
+        $this->cache[$key] = $jwt_body;
+        $this->save_cache();
         return $this;
     }
 
     public function cache_nonce($nonce) {
-        $_SESSION['nonce'][$nonce] = true;
+        $this->cache['nonce'][$nonce] = true;
+        $this->save_cache();
         return $this;
     }
 
     public function check_nonce($nonce) {
-        if (!isset($_SESSION['nonce'][$nonce])) {
+        $this->load_cache();
+        if (!isset($this->cache['nonce'][$nonce])) {
             return false;
         }
-        unset($_SESSION['nonce'][$nonce]);
         return true;
     }
+
+    private function load_cache() {
+        $cache = file_get_contents(sys_get_temp_dir() . '/lti_cache.txt');
+        if (empty($cache)) {
+            file_put_contents(sys_get_temp_dir() . '/lti_cache.txt', '{}');
+            $this->cache = [];
+        }
+        $this->cache = json_decode($cache, true);
+    }
+
+    private function save_cache() {
+        file_put_contents(sys_get_temp_dir() . '/lti_cache.txt', json_encode($this->cache));
+    }
 }
 ?>

src/lti/LTI_OIDC_Login.php

@@ -62,7 +62,7 @@ public function do_oidc_login_redirect($launch_url, array $request = null) {
         // Generate State.
         // Set cookie (short lived)
         $state = str_replace('.', '_', uniqid('state-', true));
-        $this->cookie->set_cookie("lti1p3_$state", $state);
+        $this->cookie->set_cookie("lti1p3_$state", $state, 60);
 
         // Generate Nonce.
         $nonce = uniqid('nonce-', true);