base.rb

class FormObjectBase
 include ::ActiveModel::Validations

 attr_reader :object, :params

 def initialize(object)
   @object = object
 end

 def assign(params)
   raise 'implement it and return self'
   self
 end

 def validate
   if valid?
     if object.valid?
       true
     else
       inherit_errors
       false
     end
   else
     false
   end
 end

 def submit(options = { validate: true })
   if !options[:validate] || validate
     save
   else
     false
   end
 end

 private

 def save
   if object.save
     true
   else
     delegate_errors
     false
   end
 end

 # take errors in the model directly
 def inherit_errors
   object.errors.each do |key, value|
     errors.add(key, value)
   end
 end
end

controller.rb

form_object = ::WordersAdmin::FormObjects::User.new(user)
if form_object.assign(params.permit!).submit  # its filtered in the form object, so no pb

user_signup.rb

class UserSignup < ::FormObjectBase

  FIELDS = [
    :email, :first_name, :last_name
  ]
  
  validates :first_name, presence: true
  validates :last_name,  presence: true

  def assign(params)
    @params = params

    object.attributes = params.slice *FIELDS
    self
  end
end