Add authentication

app/models/current.rb

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+class Current < ActiveSupport::CurrentAttributes
+  attribute :session
+  delegate :user, to: :session, allow_nil: true
+end

app/models/session.rb

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+class Session < ApplicationRecord
+  belongs_to :user
+end

app/models/user.rb

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+class User < ApplicationRecord
+  has_secure_password
+  has_many :sessions, dependent: :destroy
+
+  normalizes :email_address, with: ->(e) { e.strip.downcase }
+end