code: func getAuthService(c context.Context, url string) authService {
  	if s, _ := c.Value(contextKey(0)).(authService); s != nil {
  		return s
  	}
  	return &service.AuthService{URL: url}
  }
docs: // getAuthService returns authService implementation injected into the context
  // via setAuthService or *service.AuthService otherwise.