[7.x] Switch to Symfony 5 (#5157)

* Update exception handler

* Explictly specify 'lax' same site config

* Use the null secure option for session cookies

config/session.php

@@ -166,7 +166,7 @@ return [
     |
     */
 
-    'secure' => env('SESSION_SECURE_COOKIE', false),
+    'secure' => env('SESSION_SECURE_COOKIE', null),
 
     /*
     |--------------------------------------------------------------------------
@@ -194,6 +194,6 @@ return [
     |
     */
 
-    'same_site' => null,
+    'same_site' => 'lax',
 
 ];