code: func (tr *authTransport) CancelRequest(req *http.Request) {
  	type canceler interface {
  		CancelRequest(*http.Request)
  	}
  	if cr, ok := tr.RoundTripper.(canceler); ok {
  		tr.mu.Lock()
  		modReq := tr.modReq[req]
  		delete(tr.modReq, req)
  		tr.mu.Unlock()
  		cr.CancelRequest(modReq)
  	}
  }
docs: // CancelRequest cancels an in-flight request by closing its connection.