First crack

app/channels/application_cable/connection.rb

@@ -0,0 +1,16 @@
+module ApplicationCable
+  class Connection < ActionCable::Connection::Base
+    identified_by :current_user
+
+    def connect
+      set_current_user || reject_unauthorized_connection
+    end
+
+    private
+      def set_current_user
+        if session = Session.find_by(id: cookies.signed[:session_id])
+          self.current_user = session.user
+        end
+      end
+  end
+end