kubernetes/cmd/kubeadm/app/discovery/discovery.go

const TokenUser …

// For returns a kubeconfig object that can be used for doing the TLS Bootstrap with the right credentials
// Also, before returning anything, it makes sure it can trust the API Server
func For(client clientset.Interface, cfg *kubeadmapi.JoinConfiguration) (*clientcmdapi.Config, error) { … }

// DiscoverValidatedKubeConfig returns a validated Config object that specifies where the cluster is and the CA cert to trust
func DiscoverValidatedKubeConfig(dryRunClient clientset.Interface, cfg *kubeadmapi.JoinConfiguration) (*clientcmdapi.Config, error) { … }

// isHTTPSURL checks whether the string is parsable as a URL and whether the Scheme is https
func isHTTPSURL(s string) bool { … }