[Google sign-in add-on] slim down on the ID token validation
As a quickstart, the Google client API library was completely imported using composer (50Mb+). All it is being used for is to validate the ID token. This could be done equally using a generic JWT library. In addition, it needs to use the Google public key (which are rotated and should be pulled via network request). Not sure if it does any more.
Outcome should be to replace the Google client API library by just a set of files which perform the same function.
Edited by Pascal Deklerck