Support Apple Game Center Auth (#6143)

Fixes: https://github.com/parse-community/parse-server/issues/5984

src/Adapters/Auth/apple.js

@@ -1,3 +1,6 @@
+// Apple SignIn Auth
+// https://developer.apple.com/documentation/signinwithapplerestapi
+
 const Parse = require('parse/node').Parse;
 const httpsRequest = require('./httpsRequest');
 const NodeRSA = require('node-rsa');