Using Google OAuth2 from Silverlight out-of-browser application

I'm planning to access Google's APIs and do authentication using OAuth2. Since I'm going to access them from a Silverlight out-of-browser application I was wanting to know how to keep it secure enough.

I understand that keeping all the details necessary to authenticate on the client is a bit risky. By this I mean the client_id, client_secret, etc. as they could easily be obtained by someone else. So I was wondering how people get round this? Would you use a web service to initally contact Google when authenticating? If so, how can I help keep that secure so only my Silverlight client can access it?