diff --git a/cmd/tick/main.go b/cmd/tick/main.go
index 50262b9..5bd0b01 100644
--- a/cmd/tick/main.go
+++ b/cmd/tick/main.go
@@ -42,6 +42,23 @@ func resolveRegion() (string, error) {
 	return cfg.Region, nil
 }
 
+func buildAuthService(region string, streams cli.Streams) (auth.Service, error) {
+	endpoints, err := endpoint.ForRegion(region)
+	if err != nil {
+		return auth.Service{}, err
+	}
+	return auth.Service{
+		AuthorizeURL: endpoints.AuthorizeURL,
+		Exchanger: auth.Exchanger{
+			TokenURL: endpoints.TokenURL,
+		},
+		Store:   auth.FileStore{},
+		Browser: browserOpener{},
+		In:      streams.In,
+		Out:     streams.Out,
+	}, nil
+}
+
 func buildRuntime(streams cli.Streams) (*config.Store, auth.Service, *ticktick.Client, error) {
 	store, cfg, err := loadConfigStore()
 	if err != nil {
@@ -76,13 +93,15 @@ func main() {
 		Streams:        streams,
 		RegionResolver: resolveRegion,
 		LoginAuthResolver: func() (*app.AuthApp, error) {
-			store, service, _, err := buildRuntime(streams)
+			store, _, err := loadConfigStore()
 			if err != nil {
 				return nil, err
 			}
 			return &app.AuthApp{
 				ConfigStore: store,
-				Service:     service,
+				ServiceForRegion: func(region string) (app.AuthService, error) {
+					return buildAuthService(region, streams)
+				},
 			}, nil
 		},
 		AuthServiceResolver: func() (app.AuthService, error) {
diff --git a/internal/app/auth.go b/internal/app/auth.go
index 1b9fc21..8e5bc96 100644
--- a/internal/app/auth.go
+++ b/internal/app/auth.go
@@ -14,9 +14,12 @@ type AuthService interface {
 	Logout(context.Context) error
 }
 
+type AuthServiceFactory func(region string) (AuthService, error)
+
 type AuthApp struct {
-	ConfigStore *config.Store
-	Service     AuthService
+	ConfigStore      *config.Store
+	Service          AuthService
+	ServiceForRegion AuthServiceFactory
 }
 
 type LoginInput struct {
@@ -58,6 +61,17 @@ func (a AuthApp) Login(ctx context.Context, in LoginInput) error {
 	if in.ClientID == "" || in.ClientSecret == "" || in.RedirectURL == "" {
 		return errors.New("login requires client-id, client-secret, and redirect-url")
 	}
+	service := a.Service
+	if a.ServiceForRegion != nil {
+		var err error
+		service, err = a.ServiceForRegion(in.Region)
+		if err != nil {
+			return err
+		}
+	}
+	if service == nil {
+		return errors.New("auth service is unavailable")
+	}
 	if a.ConfigStore != nil {
 		cfg.ClientID = in.ClientID
 		cfg.ClientSecret = in.ClientSecret
@@ -67,7 +81,7 @@ func (a AuthApp) Login(ctx context.Context, in LoginInput) error {
 			return err
 		}
 	}
-	_, err := a.Service.Login(ctx, auth.LoginInput{
+	_, err := service.Login(ctx, auth.LoginInput{
 		ClientID:     in.ClientID,
 		ClientSecret: in.ClientSecret,
 		RedirectURL:  in.RedirectURL,
diff --git a/internal/app/auth_test.go b/internal/app/auth_test.go
index ecbf13e..b1d07b6 100644
--- a/internal/app/auth_test.go
+++ b/internal/app/auth_test.go
@@ -36,6 +36,23 @@ func (f fakeAuthService) Logout(context.Context) error {
 	return nil
 }
 
+type recordingLoginAuthService struct {
+	loginInput auth.LoginInput
+}
+
+func (r *recordingLoginAuthService) Login(_ context.Context, in auth.LoginInput) (auth.Token, error) {
+	r.loginInput = in
+	return auth.Token{AccessToken: "access-1"}, nil
+}
+
+func (r *recordingLoginAuthService) Status(context.Context) (auth.Status, error) {
+	return auth.Status{}, nil
+}
+
+func (r *recordingLoginAuthService) Logout(context.Context) error {
+	return nil
+}
+
 func TestAuthAppStatus(t *testing.T) {
 	store := config.NewStore(t.TempDir() + "/config.yaml")
 	app := AuthApp{
@@ -125,6 +142,49 @@ func TestAuthAppLoginPersistsConfigOnSuccess(t *testing.T) {
 	}
 }
 
+func TestAuthAppLoginBuildsServiceForSelectedRegion(t *testing.T) {
+	store := config.NewStore(t.TempDir() + "/config.yaml")
+	if err := store.Save(config.Config{
+		Region:       "ticktick",
+		ClientID:     "old-client-id",
+		ClientSecret: "old-secret",
+		RedirectURL:  "http://localhost:14573/callback",
+	}); err != nil {
+		t.Fatalf("Save() error = %v", err)
+	}
+
+	selectedRegion := ""
+	service := &recordingLoginAuthService{}
+	app := AuthApp{
+		ConfigStore: store,
+		ServiceForRegion: func(region string) (AuthService, error) {
+			selectedRegion = region
+			return service, nil
+		},
+	}
+
+	if err := app.Login(context.Background(), LoginInput{
+		Region:       "dida365",
+		ClientID:     "new-client-id",
+		ClientSecret: "new-secret",
+	}); err != nil {
+		t.Fatalf("Login() error = %v", err)
+	}
+	if selectedRegion != "dida365" {
+		t.Fatalf("service region = %q, want dida365", selectedRegion)
+	}
+	if service.loginInput.ClientID != "new-client-id" {
+		t.Fatalf("ClientID = %q, want new-client-id", service.loginInput.ClientID)
+	}
+	cfg, err := store.Load()
+	if err != nil {
+		t.Fatalf("Load() error = %v", err)
+	}
+	if cfg.Region != "dida365" {
+		t.Fatalf("stored Region = %q, want dida365", cfg.Region)
+	}
+}
+
 func TestAuthAppLoginSucceedsWithoutConfigStoreWhenInputsAreExplicit(t *testing.T) {
 	app := AuthApp{
 		Service: fakeAuthService{},