Refactor

auth/authcode.go

@@ -0,0 +1,107 @@
+package auth
+
+import (
+	"context"
+	"crypto/rand"
+	"encoding/binary"
+	"fmt"
+	"log"
+	"net/http"
+
+	"golang.org/x/oauth2"
+)
+
+// BrowserAuthCodeFlow is a flow to get a token by browser interaction.
+type BrowserAuthCodeFlow struct {
+	oauth2.Config
+	Port int // HTTP server port
+}
+
+// GetToken returns a token.
+func (f *BrowserAuthCodeFlow) GetToken(ctx context.Context) (*oauth2.Token, error) {
+	f.Config.RedirectURL = fmt.Sprintf("http://localhost:%d/", f.Port)
+	state, err := generateState()
+	if err != nil {
+		return nil, fmt.Errorf("Could not generate state parameter: %s", err)
+	}
+	log.Printf("Open http://localhost:%d for authorization", f.Port)
+	code, err := f.getCode(ctx, &f.Config, state)
+	if err != nil {
+		return nil, err
+	}
+	token, err := f.Config.Exchange(ctx, code)
+	if err != nil {
+		return nil, fmt.Errorf("Could not exchange oauth code: %s", err)
+	}
+	return token, nil
+}
+
+func generateState() (string, error) {
+	var n uint64
+	if err := binary.Read(rand.Reader, binary.LittleEndian, &n); err != nil {
+		return "", err
+	}
+	return fmt.Sprintf("%x", n), nil
+}
+
+func (f *BrowserAuthCodeFlow) getCode(ctx context.Context, config *oauth2.Config, state string) (string, error) {
+	codeCh := make(chan string)
+	errCh := make(chan error)
+	server := http.Server{
+		Addr: fmt.Sprintf(":%d", f.Port),
+		Handler: &handler{
+			AuthCodeURL: config.AuthCodeURL(state),
+			Callback: func(code string, actualState string, err error) {
+				switch {
+				case err != nil:
+					errCh <- err
+				case actualState != state:
+					errCh <- fmt.Errorf("OAuth state did not match, should be %s but %s", state, actualState)
+				default:
+					codeCh <- code
+				}
+			},
+		},
+	}
+	go func() {
+		if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+			errCh <- err
+		}
+	}()
+	select {
+	case err := <-errCh:
+		server.Shutdown(ctx)
+		return "", err
+	case code := <-codeCh:
+		server.Shutdown(ctx)
+		return code, nil
+	}
+}
+
+type handler struct {
+	AuthCodeURL string
+	Callback    func(code string, state string, err error)
+}
+
+func (s *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	log.Printf("%s %s", r.Method, r.RequestURI)
+	switch r.URL.Path {
+	case "/":
+		code := r.URL.Query().Get("code")
+		state := r.URL.Query().Get("state")
+		errorCode := r.URL.Query().Get("error")
+		errorDescription := r.URL.Query().Get("error_description")
+		switch {
+		case code != "":
+			s.Callback(code, state, nil)
+			fmt.Fprintf(w, "Back to command line.")
+		case errorCode != "":
+			s.Callback("", "", fmt.Errorf("OAuth Error: %s %s", errorCode, errorDescription))
+			fmt.Fprintf(w, "Back to command line.")
+		default:
+			http.Redirect(w, r, s.AuthCodeURL, 302)
+		}
+	default:
+		http.Error(w, "Not Found", 404)
+	}
+}