code: func (m *Manager) GetClient(clientID, label string) (client *Oauth2Client, err error) {
  	client = &Oauth2Client{}
  	err = m.getClientsCollection().Find(bson.M{"clientid": clientID, "label": label}).One(client)
  	if err == mgo.ErrNotFound {
  		err = nil
  		client = nil
  		return
  	}
  	return
  }
docs: //GetClient retrieves a client given a clientid and a label