fix(backend): resolve signup issues by fixing tenant slug case-sensitivity and exposing Kratos errors

backend/internal/handler/auth_handler.go

@@ -473,6 +473,8 @@ func (h *AuthHandler) Signup(c *fiber.Ctx) error {
 		normalizedPhone = "+" + normalizedPhone
 	}
 
+	slog.Info("[Signup] Phone normalization", "raw", req.Phone, "normalized", normalizedPhone)
+
 	// IDP에 전달할 BrokerUser 스키마 구성
 	attributes := map[string]interface{}{
 		"department":      req.Department,
@@ -517,7 +519,8 @@ func (h *AuthHandler) Signup(c *fiber.Ctx) error {
 		if strings.Contains(err.Error(), "already exists") {
 			return errorJSON(c, fiber.StatusConflict, "User already exists")
 		}
-		return errorJSON(c, fiber.StatusInternalServerError, "Failed to create user")
+		// Include the actual error message in the response for debugging
+		return errorJSON(c, fiber.StatusInternalServerError, fmt.Sprintf("Failed to create user: %v", err))
 	}
 
 	// 4. Cleanup Redis

backend/internal/repository/tenant_repository.go

@@ -3,6 +3,7 @@ package repository
 import (
 	"baron-sso-backend/internal/domain"
 	"context"
+	"strings"
 
 	"gorm.io/gorm"
 )
@@ -45,7 +46,7 @@ func (r *tenantRepository) FindByID(ctx context.Context, id string) (*domain.Ten
 
 func (r *tenantRepository) FindBySlug(ctx context.Context, slug string) (*domain.Tenant, error) {
 	var tenant domain.Tenant
-	if err := r.db.WithContext(ctx).Preload("Domains").Where("slug = ?", slug).First(&tenant).Error; err != nil {
+	if err := r.db.WithContext(ctx).Preload("Domains").Where("slug = ?", strings.ToLower(slug)).First(&tenant).Error; err != nil {
 		return nil, err
 	}
 	return &tenant, nil