Google has a very complete OAuth2 Java library that you can use to set up an application to request tokens. However, all OAuth flows require user interaction to authenticate with the provider; you can not access their data until authorization is granted.
Quick question to help with is the Authorization is once it is required or every time we make a request? while calling each end point
With integrations from other apps (such as woocommerce, clickfunnels etc.,) I hope the authorization is one time (otherwise, how the integrations are working?)