I found this question on the website and according to it, the subscriptions of Google Play uses same receipt to renew the subscriptions.
I guess, this means that when a subscription of a player renews itself, it doesn't generate a new receipt ID. I just need to check the old one to see if it's valid. If this is correct, accessing validate APIs on Cloudscript can make the auto-renew subscriptions process autonomous on the server side.
I create an empty item that is consumable by time (1 month), and I also save receipt ID of the subscription on the player's internal data.
After a month, the item disappears on the player's inventory and it will trigger player_consumed_item event. Then I check the player's receipt ID on Cloudscript to see if the player's subscription is still active.