In this article, the steps of logining with 3rd party authentication are -
1. Does 3rd part authenticate. Get an identify unique string like access token after login success.
2. Maps this identify unique string into username and password by looking up table stored in parse server
3. Uses username and password to login parse.
So the concept is: getting an unique username for built-in parse logining.
But the question is - how to run step1 to do 3rd party authentication?
My solution is using firebase's authentication first, then login parse.
1. firebase supports authentication by facebook, google, twitter, github. After login with one of these authentication, firebase will have an "UserID" which is an unique string for each user. (plugin of authentication in firebase)
2. Pass username to "UserID", password to access token (or mapping "UserID" or access token to another username-password pair) to login parse.
(Now user had login firebase and parse)
I had tested these steps already.