Allow protectedFields for Authenticated users and Public. Fix userField with keys/excludedKeys (#6415)

* fix error message and test it

* protected fields fixes

* clean

* remove duplicate test, add some comments

* no need for 'requiresAuthentication'

src/Routers/ClassesRouter.js

@@ -6,6 +6,7 @@ import Parse from 'parse/node';
 const ALLOWED_GET_QUERY_KEYS = [
   'keys',
   'include',
+  'excludeKeys',
   'readPreference',
   'includeReadPreference',
   'subqueryReadPreference',
@@ -69,6 +70,9 @@ export class ClassesRouter extends PromiseRouter {
     if (body.include) {
       options.include = String(body.include);
     }
+    if (typeof body.excludeKeys == 'string') {
+      options.excludeKeys = body.excludeKeys;
+    }
     if (typeof body.readPreference === 'string') {
       options.readPreference = body.readPreference;
     }