fixes #2389

app/controllers/application_controller.rb

@@ -14,6 +14,7 @@ class ApplicationController < ActionController::Base
 
   rescue_from Exception, :with => :rescue_exception
   rescue_from User::PrivilegeError, :with => :access_denied
+  rescue_from SessionLoader::AuthenticationFailure, :with => :authentication_failed
   rescue_from Danbooru::Paginator::PaginationError, :with => :render_pagination_limit
 
 protected
@@ -47,6 +48,18 @@ protected
     render :template => "static/error", :status => 410
   end
 
+  def authentication_failed
+    respond_to do |fmt|
+      fmt.html do
+        render :text => "authentication failed", :status => 401
+      end
+
+      fmt.json do
+        render :json => {:success => false, :reason => "authentication failed"}, :status => 401
+      end
+    end
+  end
+
   def access_denied(exception = nil)
     previous_url = params[:url] || request.fullpath