added AuthenticationToken model, updated some restrictions for the authentication token table, added dependent destroy to the user model for authentication tokens

app/models/authentication_token.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require 'securerandom'
+
+class AuthenticationToken < ApplicationRecord
+  include Creation
+  def self.generate!(user)
+    create!(
+      shared_secret: SecureRandom.hex(32),
+      user: user,
+      expire_at: 7.days.from_now
+    )
+  end
+end