I use: oauth2client.client.GoogleCredentials
cred = oauth2client.client.GoogleCredentials(access_token,client_id,client_secret,
refresh_token,expires_at,"https://accounts.google.com/o/oauth2/token",some_user_agent)
http = cred.authorize(httplib2.Http())
cred.refresh(http)
self.gmail_service = discovery.build('gmail', 'v1', credentials=cred)