work off today

config/initializers/devise.rb

@@ -1,5 +1,19 @@
-# Use this hook to configure devise mailer, warden hooks and so forth.
-# Many of these configuration options can be set straight in your model.
+module Qwaiter
+  class FailureApp < Devise::FailureApp
+    def respond
+      if request.format.json?
+        json_api_error_response
+      else
+        super
+      end
+    end
+    def json_api_error_response
+      self.status        = 401
+      self.content_type  = 'application/json'
+      self.response_body = { errors: [{ status: '401', title: i18n_message }]}.to_json
+    end
+  end
+end
 Devise.setup do |config|
   # The secret key used by Devise. Devise uses this key to generate
   # random tokens. Changing this key will render invalid all existing
@@ -250,10 +264,11 @@ Devise.setup do |config|
   # If you want to use other strategies, that are not supported by Devise, or
   # change the failure app, you can configure them inside the config.warden block.
   #
-  # config.warden do |manager|
+  config.warden do |manager|
+    manager.failure_app = Qwaiter::FailureApp
   #   manager.intercept_401 = false
   #   manager.default_strategies(:scope => :user).unshift :some_external_strategy
-  # end
+  end
 
   # ==> Mountable engine configurations
   # When using Devise inside an engine, let's call it `MyEngine`, and this engine