Devise は、Warden をベースにした柔軟でモジュール式の Ruby on Rails 向け本格認証ソリューションです。
インストールとジェネレーター（Installation & Generators）
# Add gem to Gemfile and bundle
bundle add devise
# Install Devise configuration initializer
rails generate devise:install
# Generate Devise model (e.g. User or Admin)
rails generate devise User
rails db:migrate
# Generate editable views
rails generate devise:views
コントローラー＆ビューヘルパー（Controller & View Helpers）
# Protect controller actions with before_action
before_action :authenticate_user!
# Status checks
user_signed_in?
current_user
user_session
# URL and Path Helpers
new_user_session_path # Login form
destroy_user_session_path # Logout (DELETE)
new_user_registration_path # Sign up form
edit_user_registration_path # Edit account settings
new_user_password_path # Password reset request
モデルモジュール一覧（Model Modules）
class User < ApplicationRecord
devise :database_authenticatable, # Hashes and stores passwords in DB
:registerable, # Sign up, edit, and destroy accounts
:recoverable, # Resets password and sends reset instructions
:rememberable, # Manages cookies to remember user sessions
:trackable, # Tracks sign in count, timestamps, and IP addresses
:validatable, # Validates email and password length/presence
:confirmable, # Sends verification emails with tokens
:lockable, # Locks accounts after failed login attempts
:timeoutable # Expires inactive sessions after set duration
end
スコープ付きルーティング（Scoped Routing）
Rails.application.routes.draw do
devise_for :users
# Custom route scopes based on authentication status
authenticated :user do
root to: 'dashboard#index', as: :authenticated_root
end
unauthenticated do
root to: 'home#index'
end
end