Add client_secret.json
Add client_secret.json

According to Google (https://developers.google.com/identity/protocols/OAuth2InstalledApp)
we can include the client secret in the installed app:

> The client ID and client secret obtained from the Developers Console
> are embedded in the source code of your application. In this context,
> the client secret is obviously not treated as a secret.

metaodi/cabdriver