fs: change Config callback into state based callback #3455

This is a very large change which turns the post Config function in
backends into a state based call and response system so that
alternative user interfaces can be added.

The existing config logic has been converted, but it is quite
complicated and folloup commits will likely be needed to fix it!

Follow up commits will add a command line and API based way of using
this configuration system.

backend/seafile/seafile.go

@@ -296,83 +296,86 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (fs.Fs, e
 }
 
 // Config callback for 2FA
-func Config(ctx context.Context, name string, m configmap.Mapper) error {
-	ci := fs.GetConfig(ctx)
+func Config(ctx context.Context, name string, m configmap.Mapper, config fs.ConfigIn) (*fs.ConfigOut, error) {
 	serverURL, ok := m.Get(configURL)
 	if !ok || serverURL == "" {
 		// If there's no server URL, it means we're trying an operation at the backend level, like a "rclone authorize seafile"
-		return errors.New("operation not supported on this remote. If you need a 2FA code on your account, use the command: nrclone config reconnect <remote name>: ")
-	}
-
-	// Stop if we are running non-interactive config
-	if ci.AutoConfirm {
-		return nil
+		return nil, errors.New("operation not supported on this remote. If you need a 2FA code on your account, use the command: rclone config reconnect <remote name>: ")
 	}
 
 	u, err := url.Parse(serverURL)
 	if err != nil {
-		return errors.Errorf("invalid server URL %s", serverURL)
+		return nil, errors.Errorf("invalid server URL %s", serverURL)
 	}
 
 	is2faEnabled, _ := m.Get(config2FA)
 	if is2faEnabled != "true" {
-		return errors.New("two-factor authentication is not enabled on this account")
+		return nil, errors.New("two-factor authentication is not enabled on this account")
 	}
 
 	username, _ := m.Get(configUser)
 	if username == "" {
-		return errors.New("a username is required")
+		return nil, errors.New("a username is required")
 	}
 
 	password, _ := m.Get(configPassword)
 	if password != "" {
 		password, _ = obscure.Reveal(password)
 	}
-	// Just make sure we do have a password
-	for password == "" {
-		fmt.Print("Two-factor authentication: please enter your password (it won't be saved in the configuration)\npassword> ")
-		password = config.ReadPassword()
-	}
 
-	// Create rest client for getAuthorizationToken
-	url := u.String()
-	if !strings.HasPrefix(url, "/") {
-		url += "/"
-	}
-	srv := rest.NewClient(fshttp.NewClient(ctx)).SetRoot(url)
-
-	// We loop asking for a 2FA code
-	for {
-		code := ""
-		for code == "" {
-			fmt.Print("Two-factor authentication: please enter your 2FA code\n2fa code> ")
-			code = config.ReadLine()
+	switch config.State {
+	case "":
+		// Just make sure we do have a password
+		if password == "" {
+			return fs.ConfigPassword("", "Two-factor authentication: please enter your password (it won't be saved in the configuration)")
+		}
+		return fs.ConfigGoto("password")
+	case "password":
+		password = config.Result
+		if password == "" {
+			return fs.ConfigError("password", "Password can't be blank")
+		}
+		m.Set(configPassword, obscure.MustObscure(config.Result))
+		return fs.ConfigGoto("2fa")
+	case "2fa":
+		return fs.ConfigInput("2fa_do", "Two-factor authentication: please enter your 2FA code")
+	case "2fa_do":
+		code := config.Result
+		if code == "" {
+			return fs.ConfigError("2fa", "2FA codes can't be blank")
 		}
 
+		// Create rest client for getAuthorizationToken
+		url := u.String()
+		if !strings.HasPrefix(url, "/") {
+			url += "/"
+		}
+		srv := rest.NewClient(fshttp.NewClient(ctx)).SetRoot(url)
+
+		// We loop asking for a 2FA code
 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 		defer cancel()
 
-		fmt.Println("Authenticating...")
 		token, err := getAuthorizationToken(ctx, srv, username, password, code)
 		if err != nil {
-			fmt.Printf("Authentication failed: %v\n", err)
-			tryAgain := strings.ToLower(config.ReadNonEmptyLine("Do you want to try again (y/n)?"))
-			if tryAgain != "y" && tryAgain != "yes" {
-				// The user is giving up, we're done here
-				break
-			}
+			return fs.ConfigConfirm("2fa_error", true, fmt.Sprintf("Authentication failed: %v\n\nTry Again?", err))
 		}
-		if token != "" {
-			fmt.Println("Success!")
-			// Let's save the token into the configuration
-			m.Set(configAuthToken, token)
-			// And delete any previous entry for password
-			m.Set(configPassword, "")
-			// And we're done here
-			break
+		if token == "" {
+			return fs.ConfigConfirm("2fa_error", true, "Authentication failed - no token returned.\n\nTry Again?")
 		}
+		// Let's save the token into the configuration
+		m.Set(configAuthToken, token)
+		// And delete any previous entry for password
+		m.Set(configPassword, "")
+		// And we're done here
+		return nil, nil
+	case "2fa_error":
+		if config.Result == "true" {
+			return fs.ConfigGoto("2fa")
+		}
+		return nil, errors.New("2fa authentication failed")
 	}
-	return nil
+	return nil, fmt.Errorf("unknown state %q", config.State)
 }
 
 // sets the AuthorizationToken up