Refactor ID card sign-in

- Extract to Devise custom strategy
- Use `SSL_CLIENT_S_DN_CN` env variable instead of `SSL_CLIENT_S_DN` to
get ID card data
- Remove `database_authenticatable` strategy from `RegistrantUser`

Closes #1047

lib/devise/models/id_card_authenticatable.rb

@@ -0,0 +1,7 @@
+module Devise
+  module Models
+    # Devise fails without this module (and model: false does not help)
+    module IdCardAuthenticatable
+    end
+  end
+end

lib/devise/strategies/id_card_authenticatable.rb

@@ -0,0 +1,49 @@
+module Devise
+  module Strategies
+    class IdCardAuthenticatable < Devise::Strategies::Authenticatable
+      def valid?
+        env['SSL_CLIENT_S_DN_CN'].present?
+      end
+
+      def authenticate!
+        resource = mapping.to
+        user = resource.find_by_id_card(id_card)
+
+        if user
+          success!(user)
+        else
+          fail
+        end
+      end
+
+      private
+
+      def id_card
+        id_card = IdCard.new
+        id_card.first_name = first_name
+        id_card.last_name = last_name
+        id_card.personal_code = personal_code
+        id_card.country_code = country_code
+        id_card
+      end
+
+      def first_name
+        env['SSL_CLIENT_S_DN_CN'].split(',').second.force_encoding('utf-8')
+      end
+
+      def last_name
+        env['SSL_CLIENT_S_DN_CN'].split(',').first.force_encoding('utf-8')
+      end
+
+      def personal_code
+        env['SSL_CLIENT_S_DN_CN'].split(',').last
+      end
+
+      def country_code
+        env['SSL_CLIENT_I_DN_C']
+      end
+    end
+  end
+end
+
+Warden::Strategies.add(:id_card_authenticatable, Devise::Strategies::IdCardAuthenticatable)