code: func (m *Manager) GetAccessToken(token string) (at *AccessToken, err error) {
  	at = &AccessToken{}
  
  	err = m.getAccessTokenCollection().Find(bson.M{"accesstoken": token}).One(at)
  	if err != nil && err == mgo.ErrNotFound {
  		at = nil
  		err = nil
  		return
  	}
  	if err != nil {
  		at = nil
  		return
  	}
  	if at.IsExpired() {
  		at = nil
  		err = nil
  	}
  
  	return
  }
docs: //GetAccessToken gets an access token by it's actual token string
  // If the token is not found or is expired, nil is returned