Allow Mastodon address domain to be different from primary domain

app/models/user.rb

@@ -110,6 +110,11 @@ class User < ApplicationRecord
     "#{self.cn}@#{self.ou}"
   end
 
+  def mastodon_address
+    return nil unless Setting.mastodon_enabled?
+    "#{self.cn}@#{Setting.mastodon_address_domain}"
+  end
+
   def valid_attribute?(attribute_name)
     self.valid?
     self.errors[attribute_name].blank?