♻️ Ensure users cannot register on their own

Related to:

- https://github.com/scientist-softserv/adventist-dl/issues/492
- https://github.com/scientist-softserv/adventist-dl/issues/618
- samvera/hyku#1964
- scientist-softserv/adventist-dl#493
- samvera/hyku#2020

lib/hyku_knapsack/engine.rb

@@ -31,6 +31,18 @@ def self.load_translations!
 
     config.before_initialize do
       config.i18n.load_path += Dir["#{config.root}/config/locales/**/*.yml"]
+
+      if Hyku::Application.respond_to?(:user_devise_parameters=)
+        Hyku::Application.user_devise_parameters = %i[
+          database_authenticatable
+          invitable
+          recoverable
+          rememberable
+          trackable
+          validatable
+          omniauthable
+        ]
+      end
     end
 
     ##

spec/hyku_knapsack/engine_spec.rb

@@ -3,6 +3,12 @@
 require 'spec_helper'
 
 RSpec.describe HykuKnapsack::Engine do
+  describe 'Devise configuration' do
+    subject { Devise.mappings[:user] }
+
+    it { is_expected.not_to be_registerable }
+  end
+
   describe 'I18n.load_path' do
     it 'has HykuKnapsack translations at a higher precendence than Hyku translations' do
       hyku_root = Rails.root.to_s