PGSGP: Backend Token Verification – [Server-side] extension for increased security

[Star-Frog]

I made the two following requests about a year ago in the original PGSGP, I think that such an extension or creation (of a server-side module) could be of great importance, especially for Godot-Android developers, and a great contribution to the security of the application can afford.

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I would like to integrate token authentication on the server side for the PlayGamesServices so that only the server can make calls.
"Never trust the client" ;)

Seems to be a common practice:
https://developer.android.com/games/pgs/android/server-access

Here is a graphic (for better understanding):
https://developer.android.com/games/playgames/integrating-pgs-existing-id-solutions#restore_player_state

How can I have the token received - (on the backend) from the client - exchanged for the access token at Google Play Games Services. Is there a module for this or another solution? Thanks in advance! :)

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GooglePlayServices (client-server model):
Does anyone know how to check my client's token on my game-server? Is there a module for Godot for this? (I also have to connect my server to "Google Play Games Services" and query the token there, right?)
🤔

Two more official links:

Official Google source about the server side (section): https://developers.google.com/games/services/android/offline-access#exchange_the_server_auth_code_for_an_access_token_on_the_server

Source of example code:
https://github.com/playgameservices/clientserverskeleton/tree/master/ServerApp/src/main/java/com/google/sample/games