Component	Purpose	Reference
User model	Password hashing with bcrypt	models.md
Session model	Track active sessions	models.md
Current model	Request-scoped attributes	models.md
Authentication concern	Controller authentication	controllers.md
SessionsController	Login/logout endpoints	controllers.md
Login view	Sign-in form	views.md
Migrations	Database schema	migrations.md
I18n translations	User-facing strings	i18n.md

Minimal Implementation

User Model

class User < ApplicationRecord
  has_secure_password
  has_many :sessions, dependent: :destroy
  normalizes :email_address, with: ->(e) { e.strip.downcase }
  validates :email_address, presence: true, uniqueness: { case_sensitive: false }
end

Session Model

class Session < ApplicationRecord
  belongs_to :user
end

Current Model

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

Authentication Concern

module Authentication
  extend ActiveSupport::Concern
  included do
    before_action :require_authentication
  end

  class_methods do
    def allow_unauthenticated_access(**options)
      skip_before_action :require_authentication, **options
    end
  end

  private

  def require_authentication
    resume_session || request_authentication
  end

  def resume_session
    Current.session ||= find_session_by_cookie
  end

  def find_session_by_cookie
    Session.find_by(id: cookies.signed[:session_id])
  end

  def request_authentication
    session[:return_to_after_authenticating] = request.url
    redirect_to new_session_path
  end

  def start_new_session_for(user)
    user.sessions.create!(user_agent: request.user_agent, ip_address: request.remote_ip).tap do |session|
      Current.session = session
      cookies.signed.permanent[:session_id] = { value: session.id, httponly: true, same_site: :lax }
    end
  end

  def terminate_session
    Current.session.destroy
    cookies.delete(:session_id)
  end
end

Sessions Controller

class SessionsController < ApplicationController
  allow_unauthenticated_access only: %i[new create]
  rate_limit to: 10, within: 3.minutes, only: :create,
             with: -> { redirect_to new_session_url, alert: t("sessions.flash.rate_limit") }

  def new; end

  def create
    if user = User.authenticate_by(params.permit(:email_address, :password))
      start_new_session_for user
      redirect_to after_authentication_url, notice: t("sessions.flash.create.success")
    else
      redirect_to new_session_path, alert: t("sessions.flash.create.error")
    end
  end

  def destroy
    terminate_session
    redirect_to new_session_path, notice: t("sessions.flash.destroy.success")
  end

  private

  def after_authentication_url
    session.delete(:return_to_after_authenticating) || root_url
  end
end

Routes

Rails.application.routes.draw do
  resource :session  # new, create, destroy
end

Security Features

Signed cookies: Tamper-proof session storage
HttpOnly: Prevents JavaScript access (XSS protection)
SameSite: :lax: CSRF protection
Rate limiting: Built-in brute force protection
bcrypt hashing: Secure password storage

Detailed References

For complete implementation details:

models.md: Full model code with validations and associations
controllers.md: Complete controller implementations with Bearer token support
views.md: Login form templates with proper autocomplete attributes
migrations.md: Database migrations for users and sessions
i18n.md: Translation keys for all user-facing strings
security.md: Security best practices and considerations

rails8-authentication

Rails 8 Built-in Authentication

Quick Start

Core Components