Add option for skipping secret generation (#56)

* Add option for skipping secret generation

* Use #nil?

* Send options to callbacks

lib/active_model/one_time_password.rb

@@ -15,7 +15,7 @@ def has_one_time_password(options = {})
 
         include InstanceMethodsOnActivation
 
-        before_create do
+        before_create(options.slice(:if, :unless)) do
           self.otp_regenerate_secret if !otp_column
           self.otp_regenerate_counter if otp_counter_based && !otp_counter
         end

test/models/opt_in_two_factor.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class OptInTwoFactor
+  extend ActiveModel::Callbacks
+  include ActiveModel::Validations
+  include ActiveModel::OneTimePassword
+
+  define_model_callbacks :create
+  attr_accessor :otp_secret_key, :email
+
+  has_one_time_password unless: :otp_opt_in?
+
+  def otp_opt_in?
+    true
+  end
+end

test/one_time_password_test.rb

@@ -17,6 +17,10 @@ def setup
     @ar_user = ActiverecordUser.new
     @ar_user.email = '[email protected]'
     @ar_user.run_callbacks :create
+
+    @opt_in = OptInTwoFactor.new
+    @opt_in.email = '[email protected]'
+    @opt_in.run_callbacks :create
   end
 
   def test_authenticate_with_otp
@@ -49,6 +53,14 @@ def test_counter_based_otp_active_record
     assert code != @ar_user.otp_code(auto_increment: true)
   end
 
+  def test_opt_in_two_factor
+    assert @opt_in.otp_column.nil?
+
+    @opt_in.otp_regenerate_secret
+    code = @opt_in.otp_code
+    assert @opt_in.authenticate_otp(code)
+  end
+
   def test_authenticate_with_otp_when_drift_is_allowed
     code = @user.otp_code(Time.now - 30)
     assert @user.authenticate_otp(code, drift: 60)