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/models/identity.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+# == Schema Information
+#
+# Table name: identities
+#
+#  id         :integer          not null, primary key
+#  user_id    :integer
+#  provider   :string           default(""), not null
+#  uid        :string           default(""), not null
+#  created_at :datetime         not null
+#  updated_at :datetime         not null
+#
+
+class Identity < ApplicationRecord
+  belongs_to :user, dependent: :destroy
+  validates :uid, presence: true, uniqueness: { scope: :provider }
+  validates :provider, presence: true
+
+  def self.find_for_oauth(auth)
+    find_or_create_by(uid: auth.uid, provider: auth.provider)
+  end
+end