Add OAuth scopes

https://github.com/foodcoops/foodsoft/issues/582#issuecomment-442513237

config/initializers/doorkeeper.rb

@@ -47,8 +47,13 @@ Doorkeeper.configure do
   # Define access token scopes for your provider
   # For more information go to
   # https://github.com/doorkeeper-gem/doorkeeper/wiki/Using-Scopes
-  # default_scopes  :public
-  # optional_scopes :write, :update
+
+  # default is a collection of read-only scopes
+  default_scopes 'config:user', 'user:read'
+
+  optional_scopes 'config:read', 'config:write',
+                  'user:write',
+                  'offline_access'
 
   # Change the way client credentials are retrieved from the request object.
   # By default it retrieves first from the `HTTP_AUTHORIZATION` header, then