Throw error when setting authData to null (#6154)

* added ignore authData field

* add fix for Postgres

* add test for mongoDB

* add test login with provider despite invalid authData

* removed fit

* fixed ignoring authData in postgres

* Fix postgres test

* Throw error instead of ignore

* improve tests

* Add mongo test

* allow authData when not user class

* fix tests

* more tests

* add condition to synthesize authData field only in _User class

it is forbidden to add a custom field name beginning with `_`, so if the object is not `_User` , the transform should throw

* add warning log when ignoring invalid `authData` in `_User`

* add test to throw when custom field begins with underscore

src/Adapters/Storage/Mongo/MongoTransform.js

@@ -1403,10 +1403,19 @@ const mongoObjectToParseObject = (className, mongoObject, schema) => {
           case 'times_used':
             restObject['timesUsed'] = mongoObject[key];
             break;
+          case 'authData':
+            if (className === '_User') {
+              log.warn(
+                'ignoring authData in _User as this key is reserved to be synthesized of `_auth_data_*` keys'
+              );
+            } else {
+              restObject['authData'] = mongoObject[key];
+            }
+            break;
           default:
             // Check other auth data keys
             var authDataMatch = key.match(/^_auth_data_([a-zA-Z0-9_]+)$/);
-            if (authDataMatch) {
+            if (authDataMatch && className === '_User') {
               var provider = authDataMatch[1];
               restObject['authData'] = restObject['authData'] || {};
               restObject['authData'][provider] = mongoObject[key];