// Do watches for unauthorized challenges.  If we know to respond, we respond to the challenge
func (client *challengingClient) Do(req *http.Request) (*http.Response, error) {
	// Set custom header required by server to avoid CSRF attacks on browsers using basic auth
	if req.Header == nil {
		req.Header = http.Header{}
	}
	req.Header.Set(CSRFTokenHeader, "1")

	resp, err := client.delegate.Do(req)
	if err != nil {
		return nil, err
	}

	if resp.StatusCode == http.StatusUnauthorized {
		if wantsBasicAuth, realm := isBasicAuthChallenge(resp); wantsBasicAuth {
			username := client.defaultUsername
			password := client.defaultPassword

			missingUsername := len(username) == 0
			missingPassword := len(password) == 0

			url := *req.URL
			url.Path, url.RawQuery, url.Fragment = "", "", ""

			if (missingUsername || missingPassword) && client.reader != nil {
				fmt.Printf("Authentication required for %s (%s)\n", &url, realm)
				if missingUsername {
					username = util.PromptForString(client.reader, "Username: "******"Password: ")
				}
			}

			if len(username) > 0 || len(password) > 0 {
				client.delegate.Transport = kclient.NewBasicAuthRoundTripper(username, password, client.delegate.Transport)
				return client.delegate.Do(resp.Request)
			}
		}
	}
	return resp, err
}
// Negotiate a bearer token with the auth server, or try to reuse one based on the
// information already present. In case of any missing information, ask for user input
// (usually username and password, interactive depending on the Reader).
func (o *LoginOptions) gatherAuthInfo() error {
	directClientConfig, err := o.getClientConfig()
	if err != nil {
		return err
	}

	// make a copy and use it to avoid mutating the original
	t := *directClientConfig
	clientConfig := &t

	// if a token were explicitly provided, try to use it
	if o.tokenProvided() {
		clientConfig.BearerToken = o.Token
		if osClient, err := client.New(clientConfig); err == nil {
			me, err := whoAmI(osClient)
			if err == nil {
				o.Username = me.Name
				o.Config = clientConfig

				fmt.Fprintf(o.Out, "Logged into %q as %q using the token provided.\n\n", o.Config.Host, o.Username)
				return nil
			}

			if !kerrors.IsUnauthorized(err) {
				return err
			}

			fmt.Fprintln(o.Out, "The token provided is invalid (probably expired).\n")
		}
	}

	// if a token was provided try to make use of it
	// make sure we have a username before continuing
	if !o.usernameProvided() {
		if cmdutil.IsTerminal(o.Reader) {
			for !o.usernameProvided() {
				o.Username = cmdutil.PromptForString(o.Reader, "Username: "******"Already logged into %q as %q.\n\n", o.Config.Host, o.Username)
						}

						return nil
					}
				}
			}
		}
	}

	// if kubeconfig doesn't already have a matching user stanza...
	clientConfig.BearerToken = ""
	clientConfig.CertData = []byte{}
	clientConfig.KeyData = []byte{}
	clientConfig.CertFile = o.CertFile
	clientConfig.KeyFile = o.KeyFile
	token, err := tokencmd.RequestToken(o.Config, o.Reader, o.Username, o.Password)
	if err != nil {
		return err
	}
	clientConfig.BearerToken = token

	osClient, err := client.New(clientConfig)
	if err != nil {
		return err
	}

	me, err := whoAmI(osClient)
	if err != nil {
		return err
	}
	o.Username = me.Name
	o.Config = clientConfig
	fmt.Fprintln(o.Out, "Login successful.\n")

	return nil
}