Check for a `Hash` when using the `authentication_keys` to generate the FailureApp flash message.

Fixes #3270.

lib/devise/failure_app.rb

@@ -78,7 +78,9 @@ module Devise
         options[:resource_name] = scope
         options[:scope] = "devise.failure"
         options[:default] = [message]
-        options[:authentication_keys] = scope_class.authentication_keys.join(I18n.translate(:"support.array.words_connector"))
+        auth_keys = scope_class.authentication_keys
+        keys = auth_keys.respond_to?(:keys) ? auth_keys.keys : auth_keys
+        options[:authentication_keys] = keys.join(I18n.translate(:"support.array.words_connector"))
         options = i18n_options(options)
 
         I18n.t(:"#{scope}.#{message}", options)

test/failure_app_test.rb

@@ -109,6 +109,13 @@ class FailureTest < ActiveSupport::TestCase
       assert_equal 'http://test.host/users/sign_in', @response.second["Location"]
     end
 
+    test 'supports authentication_keys as a Hash for the flash message' do
+      swap Devise, authentication_keys: { email: true, login: true } do
+        call_failure('warden' => OpenStruct.new(message: :invalid))
+        assert_equal 'Invalid email, login or password.', @request.flash[:alert]
+      end
+    end
+
     test 'uses custom i18n options' do
       call_failure('warden' => OpenStruct.new(message: :does_not_exist), app: FailureWithI18nOptions)
       assert_equal 'User Steve does not exist', @request.flash[:alert]