Add password challenge to 2FA settings, e-mail notifications (#11878)

Fix #3961

app/models/form/challenge.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class Form::Challenge
+  include ActiveModel::Model
+
+  attr_accessor :current_password, :current_username,
+                :return_to
+end

app/models/user.rb

@@ -264,17 +264,20 @@ class User < ApplicationRecord
   end
 
   def password_required?
-    return false if Devise.pam_authentication || Devise.ldap_authentication
+    return false if external?
+
     super
   end
 
   def send_reset_password_instructions
-    return false if encrypted_password.blank? && (Devise.pam_authentication || Devise.ldap_authentication)
+    return false if encrypted_password.blank?
+
     super
   end
 
   def reset_password!(new_password, new_password_confirmation)
-    return false if encrypted_password.blank? && (Devise.pam_authentication || Devise.ldap_authentication)
+    return false if encrypted_password.blank?
+
     super
   end