func (t *Transport) CancelRequest(req *http.Request) {
	cancelOnce.Do(func() {
		log.Printf("deprecated: golang.org/x/oauth2: Transport.CancelRequest no longer does anything; use contexts")
	})
}
CancelRequest does nothing. It used to be a legacy cancellation mechanism
but now only it only logs on first use to warn that it's deprecated.

Deprecated: use contexts for cancellation instead.
package oauth2
import (
	"errors"
	"log"
	"net/http"
	"sync"
)
type Transport struct {
	Source TokenSource
	Base http.RoundTripper
}
func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
	reqBodyClosed := false
	if req.Body != nil {
		defer func() {
			if !reqBodyClosed {
				req.Body.Close()
			}
		}()
	}
	if t.Source == nil {
		return nil, errors.New("oauth2: Transport's Source is nil")
	}
	token, err := t.Source.Token()
	if err != nil {
		return nil, err
	}
	req2 := cloneRequest(req)  
	token.SetAuthHeader(req2)
	reqBodyClosed = true
	return t.base().RoundTrip(req2)
}
var cancelOnce sync.Once