Omniauth without Devise

# Gemfile
gem 'omniauth-github', github: 'omniauth/omniauth-github', branch: 'master'
gem "omniauth-rails_csrf_protection", "~> 1.0"

# https://github.com/omniauth/omniauth
# https://github.com/settings/applications/new
# echo > config/initializers/omniauth.rb
# config/initializers/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :github, "GITHUB_ID", "GITHUB_SECRET"
end

rails g controller static_pages landing_page dashboard
rails g model User email github_uid

# config/routes.rb
  root 'static_pages#landing_page'
  get 'dashboard', to: 'static_pages#dashboard'

  get 'auth/github/callback', to: 'sessions#create'
  delete 'logout', to: 'sessions#destroy'
  # get 'login', to: redirect('/auth/github'), as: 'login'

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  protect_from_forgery with: :exception
  helper_method :current_user

  def require_authentication
    redirect_to root_path, alert: 'Requires authentication' unless user_signed_in?
  end

  def current_user
    @current_user ||= User.find(session[:user_id]) if session[:user_id]
  end

  def user_signed_in?
    # converts current_user to a boolean by negating the negation
    !!current_user
  end
end

# app/views/layouts/application.html.erb
<%= link_to 'Home', root_path %>
<% if current_user %>
  <%= current_user.email %>
  <%= link_to 'Dashboard', dashboard_path %>
  <%= button_to 'Logout', logout_path, method: :delete, data: { turbo: false } %>
<% else %>
  <%= button_to "Sign in with Github", "/auth/github", data: { turbo: false } %>
<% end %>

# app/controllers/sessions_controller.rb
class SessionsController < ApplicationController
  def create
    @user = User.from_omniauth(request.env['omniauth.auth'])
    if @user.persisted?
      session[:user_id] = @user.id
      redirect_to dashboard_path, notice: "Logged in as #{@user.email}"
    else
      redirect_to root_url, alert: 'Failure'
    end
  end

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

# app/models/user.rb
class User < ApplicationRecord
  validates :github_uid, presence: true, uniqueness: true
  validates :email, format: { with: URI::MailTo::EMAIL_REGEXP }, presence: true, uniqueness: true

  def self.from_omniauth(access_token)
    github_uid = access_token.uid
    data = access_token.info
    email = data['email']

    User.find_or_create_by(email:, github_uid:)
  end
end

# app/controllers/static_pages_controller.rb
class StaticPagesController < ApplicationController
  before_action :require_authentication, only: :dashboard

  def landing_page
  end

  def dashboard
  end
end