How to setup api keys?

Hello,
I am trying to login via google account. I am getting "no oauth client id for  imap.gmail.com" error.
I have found that the project is accessing api keys from assets/keys.txt.
So, I have created a file using my own apis keys. Also, changed client id in Android-Manifest file. But I am still facing the issue.

Please let me know the actual setup process.
Thank you.