gdsync should read client_secrets.json generated by the API console

[proppy]

Here is how it looks like for installed apps:

{
    "installed": {
        "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
        "auth_uri": "https://accounts.google.com/o/oauth2/auth",
        "client_email": "",
        "client_id": "<client_id>",
        "client_secret": "<client_secret>",
        "client_x509_cert_url": "",
        "redirect_uris": [
            "urn:ietf:wg:oauth:2.0:oob",
            "oob"
        ],
        "token_uri": "https://accounts.google.com/o/oauth2/token"
    }
}