DelegatingAuthenticationOptions TokenReview request timeout

it turns out that setting a timeout on HTTP client affect watch requests made by the delegated authentication component.
with a 10 second timeout watch requests are being re-established exactly after 10 seconds even though the default request timeout for them is ~5 minutes.

this is because if multiple timeouts were set, the stdlib picks the smaller timeout to be applied, leaving other useless.
for more details see a937729c2c/src/net/http/client.go (L364)

instead of setting a timeout on the HTTP client we should use context for cancellation.

cmd/kube-controller-manager/app/options/options_test.go

@@ -414,7 +414,7 @@ func TestAddFlags(t *testing.T) {
 		}).WithLoopback(),
 		Authentication: &apiserveroptions.DelegatingAuthenticationOptions{
 			CacheTTL:            10 * time.Second,
-			ClientTimeout:       10 * time.Second,
+			TokenRequestTimeout: 10 * time.Second,
 			WebhookRetryBackoff: apiserveroptions.DefaultAuthWebhookRetryBackoff(),
 			ClientCert:          apiserveroptions.ClientCertAuthenticationOptions{},
 			RequestHeader: apiserveroptions.RequestHeaderAuthenticationOptions{