Code is close, but not quite there!
- You're getting the auth object, but not actually passing it to your client there (you're setting it to nil).
- You seem to be passing your client secret as the API key, which will cause problems. They API key is for a "simple API access" key from the API console - you don't need to pass anything if you're using an oAuth 2.0 token. If you'd like, you can pass a Server simple API key. This actually catches incorrectly using access tokens for a different project, so can be handy, but isn't required.
- You don't need to specify a collection argument for plus.people.get
Additionally, make sure that the Google+ API is enabled under Services in the API console: http://developers.google.com/+