It is not unfortunately, that is stored encrypted inside of the retool internal DB (either in our infrastructure on the managed option, or yours in the self-hosted option). Trying to decrypt and pass those values to your resource would be more trouble and less secure than it is worth, as well as going through a separately managed gcp side "app" setup.
There is a run through here that should be pretty much the same for all google APIs though!
http://community.retool.com/t/how-to-connect-to-google-apis/1838