[Rails] omniauthしかログイン手段がなかったアプリにメールアドレスログインを実装する

# Gemfile
gem 'omniauth'
gem 'omniauth-rails_csrf_protection'
gem 'omniauth-twitter'

# config/initializers/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :twitter, Rails.application.credentials.dig(:twitter, :api_key), Rails.application.credentials.dig(:twitter, :secret_key)
end

# config/routes.rb
Rails.application.routes.draw do
  get '/auth/twitter/callback', to: 'sessions#create'
  get '/auth/failure', to: 'sessions#failure'
  get '/logout', to: 'sessions#destroy'
end

# app/controllers/sessions_controller.rb
class SessionsController < ApplicationController
  def create
    unless request.env['omniauth.auth'][:uid]
      flash[:warning] = '連携に失敗しました'
      redirect_to root_path
    end

    case request.env['omniauth.auth'][:provider].to_sym
    when :twitter
      user = User.find_or_create_from_auth_hash!(request.env['omniauth.auth']) # ここの処理は割愛しますが、Twitterのuidをもとにユーザーを検索して、存在しなければ作成します
      session[:id] = user.id if user.present?
    end

    redirect_to root_path
  end

  def failure
    redirect_to root_path
  end

  def destroy
    session[:id] = nil
    redirect_to root_path
  end
end

# db/schema.rb
create_table "users", force: :cascade do |t|
  t.string :uid, null: false
  t.string :name
  t.string :nickname, null: false
  t.string :image, null: false
  t.string :description
  t.string :email
  t.timestamps
end
add_index :users, :uid, unique: true

# Gemfile
gem 'bcrypt'

# app/models/user.rb
class User < ApplicationRecord
  has_secure_password # 追加

  def self.create_first_passwords! # 追加
    where(password_digest: nil).find_each do |user|
      user.password = SecureRandom.hex(10)
      user.save!
    end
  end
end

# db/schema.rb
create_table "users", force: :cascade do |t|
  t.string :uid, null: false
  t.string :name
  t.string :nickname, null: false
  t.string :image, null: false
  t.string :description
  t.string :email
  t.string :password_digest # 追加
  t.timestamps
end
add_index :users, :uid, unique: true

# config/routes.rb

Rails.application.routes.draw do
  get '/auth/twitter/callback', to: 'sessions#create'
  get '/auth/failure', to: 'sessions#failure'
  get '/logout', to: 'sessions#destroy'
  get '/login', to: 'sessions#new' # 追加
  post '/login', to: 'sessions#login' # 追加
end

# app/controllers/sessions_controller.rb

class SessionsController < ApplicationController
  def create
    unless request.env['omniauth.auth'][:uid]
      flash[:warning] = '連携に失敗しました'
      redirect_to root_path
    end

    case request.env['omniauth.auth'][:provider].to_sym
    when :twitter
      user = User.find_or_create_from_auth_hash!(request.env['omniauth.auth']) # ここの処理は割愛しますが、Twitterのuidをもとにユーザーを検索して、存在しなければ作成します
      session[:id] = user.id if user.present?
    end

    redirect_to root_path
  end

  def failure
    redirect_to root_path
  end

  def destroy
    session[:id] = nil
    redirect_to root_path
  end

  def new
  end

  def login
    user = User.find_by(email: params[:email])
    if user&.authenticate(params[:password])
      session[:id] = user.id
      redirect_to root_path
    else
      flash[:warning] = 'メールアドレスまたはパスワードが間違っています'
      redirect_to login_path
    end
  end
end

# app/views/sessions/new.html.haml

%h1 メールアドレスログイン

= form_with url: login_path, method: :post do |f|
  = f.label :email
  = f.email_field :email
  = f.label :password
  = f.password_field :password
  = f.submit 'ログイン'