Added session_secret setting to schema (#9953)

closes #9952 
- required by the express-session middleware

core/server/data/schema/default-settings.json

@@ -8,6 +8,9 @@
         },
         "notifications": {
             "defaultValue": "[]"
+        },
+        "session_secret": {
+            "defaultValue": null
         }
     },
     "blog": {

core/server/models/settings.js

@@ -17,7 +17,8 @@ function parseDefaultSettings() {
         defaultSettingsFlattened = {},
         dynamicDefault = {
             db_hash: uuid.v4(),
-            public_hash: crypto.randomBytes(15).toString('hex')
+            public_hash: crypto.randomBytes(15).toString('hex'),
+            session_secret: crypto.randomBytes(32).toString('hex')
         };
 
     _.each(defaultSettingsInCategories, function each(settings, categoryName) {