CAS + SAML authentication feature (#6425)

* Cas authentication feature

* Config

* Remove class_eval + Omniauth initializer

* Codeclimate review

* Codeclimate review 2

* Codeclimate review 3

* Remove uid/email reconciliation

* SAML authentication

* Clean up code

* Improve login form

* Fix code style issues

* Add locales

app/controllers/auth/omniauth_callbacks_controller.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+class Auth::OmniauthCallbacksController < Devise::OmniauthCallbacksController
+  skip_before_action :verify_authenticity_token
+
+  def self.provides_callback_for(provider)
+    provider_id = provider.to_s.chomp '_oauth2'
+
+    define_method provider do
+      @user = User.find_for_oauth(request.env['omniauth.auth'], current_user)
+
+      if @user.persisted?
+        sign_in_and_redirect @user, event: :authentication
+        set_flash_message(:notice, :success, kind: provider_id.capitalize) if is_navigational_format?
+      else
+        session["devise.#{provider}_data"] = request.env['omniauth.auth']
+        redirect_to new_user_registration_url
+      end
+    end
+  end
+
+  Devise.omniauth_configs.each_key do |provider|
+    provides_callback_for provider
+  end
+
+  def after_sign_in_path_for(resource)
+    if resource.email_verified?
+      root_path
+    else
+      finish_signup_path
+    end
+  end
+end