jottacloud: always store username in config and use it to avoid initial api request

Existing version did save username in config, but only when entering the custom
device/mountpoint sequence in config. Regardless of that, it did always look up the
username at startup with an api request.

This commit improves it so that the username will always be stored in config,
and when using standard authentication it picks it from the login token instead of
requesting it from the remote api, and also in fs constructor it picks it from config
instead of requesting it from remote api (again).

backend/jottacloud/jottacloud.go

@@ -152,7 +152,7 @@ func Config(ctx context.Context, name string, m configmap.Mapper, config fs.Conf
 		m.Set(configClientSecret, "")
 
 		srv := rest.NewClient(fshttp.NewClient(ctx))
-		token, tokenEndpoint, err := doTokenAuth(ctx, srv, loginToken)
+		token, tokenEndpoint, username, err := doTokenAuth(ctx, srv, loginToken)
 		if err != nil {
 			return nil, fmt.Errorf("failed to get oauth token: %w", err)
 		}
@@ -161,6 +161,7 @@ func Config(ctx context.Context, name string, m configmap.Mapper, config fs.Conf
 		if err != nil {
 			return nil, fmt.Errorf("error while saving token: %w", err)
 		}
+		m.Set(configUsername, username)
 		return fs.ConfigGoto("choose_device")
 	case "legacy": // configure a jottacloud backend using legacy authentication
 		m.Set("configVersion", fmt.Sprint(legacyConfigVersion))
@@ -271,22 +272,30 @@ sync or the backup section, for example, you must choose yes.`)
 		if config.Result != "true" {
 			m.Set(configDevice, "")
 			m.Set(configMountpoint, "")
+		}
+		username, userOk := m.Get(configUsername)
+		if userOk && config.Result != "true" {
 			return fs.ConfigGoto("end")
 		}
 		oAuthClient, _, err := getOAuthClient(ctx, name, m)
 		if err != nil {
 			return nil, err
 		}
-		jfsSrv := rest.NewClient(oAuthClient).SetRoot(jfsURL)
+		if !userOk {
-		apiSrv := rest.NewClient(oAuthClient).SetRoot(apiURL)
+			apiSrv := rest.NewClient(oAuthClient).SetRoot(apiURL)
-
+			cust, err := getCustomerInfo(ctx, apiSrv)
-		cust, err := getCustomerInfo(ctx, apiSrv)
+			if err != nil {
-		if err != nil {
+				return nil, err
-			return nil, err
+			}
+			username = cust.Username
+			m.Set(configUsername, username)
+			if config.Result != "true" {
+				return fs.ConfigGoto("end")
+			}
 		}
-		m.Set(configUsername, cust.Username)
 
-		acc, err := getDriveInfo(ctx, jfsSrv, cust.Username)
+		jfsSrv := rest.NewClient(oAuthClient).SetRoot(jfsURL)
+		acc, err := getDriveInfo(ctx, jfsSrv, username)
 		if err != nil {
 			return nil, err
 		}
@@ -582,10 +591,10 @@ func doLegacyAuth(ctx context.Context, srv *rest.Client, oauthConfig *oauth2.Con
 }
 
 // doTokenAuth runs the actual token request for V2 authentication
-func doTokenAuth(ctx context.Context, apiSrv *rest.Client, loginTokenBase64 string) (token oauth2.Token, tokenEndpoint string, err error) {
+func doTokenAuth(ctx context.Context, apiSrv *rest.Client, loginTokenBase64 string) (token oauth2.Token, tokenEndpoint string, username string, err error) {
 	loginTokenBytes, err := base64.RawURLEncoding.DecodeString(loginTokenBase64)
 	if err != nil {
-		return token, "", err
+		return token, "", "", err
 	}
 
 	// decode login token
@@ -593,7 +602,7 @@ func doTokenAuth(ctx context.Context, apiSrv *rest.Client, loginTokenBase64 stri
 	decoder := json.NewDecoder(bytes.NewReader(loginTokenBytes))
 	err = decoder.Decode(&loginToken)
 	if err != nil {
-		return token, "", err
+		return token, "", "", err
 	}
 
 	// retrieve endpoint urls
@@ -604,7 +613,7 @@ func doTokenAuth(ctx context.Context, apiSrv *rest.Client, loginTokenBase64 stri
 	var wellKnown api.WellKnown
 	_, err = apiSrv.CallJSON(ctx, &opts, nil, &wellKnown)
 	if err != nil {
-		return token, "", err
+		return token, "", "", err
 	}
 
 	// prepare out token request with username and password
@@ -626,14 +635,14 @@ func doTokenAuth(ctx context.Context, apiSrv *rest.Client, loginTokenBase64 stri
 	var jsonToken api.TokenJSON
 	_, err = apiSrv.CallJSON(ctx, &opts, nil, &jsonToken)
 	if err != nil {
-		return token, "", err
+		return token, "", "", err
 	}
 
 	token.AccessToken = jsonToken.AccessToken
 	token.RefreshToken = jsonToken.RefreshToken
 	token.TokenType = jsonToken.TokenType
 	token.Expiry = time.Now().Add(time.Duration(jsonToken.ExpiresIn) * time.Second)
-	return token, wellKnown.TokenEndpoint, err
+	return token, wellKnown.TokenEndpoint, loginToken.Username, err
 }
 
 // getCustomerInfo queries general information about the account
@@ -935,11 +944,17 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (fs.Fs, e
 		return err
 	})
 
-	cust, err := getCustomerInfo(ctx, f.apiSrv)
+	user, userOk := m.Get(configUsername)
-	if err != nil {
+	if userOk {
-		return nil, err
+		f.user = user
+	} else {
+		fs.Infof(nil, "Username not found in config and must be looked up, reconfigure to avoid the extra request")
+		cust, err := getCustomerInfo(ctx, f.apiSrv)
+		if err != nil {
+			return nil, err
+		}
+		f.user = cust.Username
 	}
-	f.user = cust.Username
 	f.setEndpoints()
 
 	if root != "" && !rootIsDir {