Now, I have changed the whole system configuration as suggested to suit the OAuth 2 Login module.
Right now the system specs are like below:
Core 2.5.8
Ref App 2.12.0
OAuth 2 Login 1.1.0
The earlier error has been solved and the Google sign in page is displayed initially, the sign-in also happens successfully through the Google APIs.
But after all this, back at the redirect URL the below error is seen:
Request processing failed; nested exception is error=“access_denied”, error_description=“Error requesting access token.”
The complete error log is here
I really hope this gets sorted out.
Thank you!