Fix flaw: was able to duplicate user emails because case sensitive check

controllers/users.go

@@ -109,7 +109,7 @@ func UserAdd(c *fiber.Ctx) error {
 		user.Email = data.Email
 
 		var usersEmail []models.User
-		result := db.Find(&usersEmail, "email = ?", user.Email)
+		result := db.Find(&usersEmail, "LOWER(email) = LOWER(?)", user.Email)
 		if result.Error != nil {
 			return result.Error
 		}