ftp-manager/app/controllers/auth_controller.rb

class AuthController < ApplicationController
  skip_before_action :verify_session

  def login
  end

  def logout
    session.destroy
    redirect_to login_path
  end

  def auth
    redirect_to client.auth_code.authorize_url(redirect_uri: ENV['callback_url'])
  end

  def callback
    access_token = client.auth_code.get_token(params[:code], redirect_uri: ENV['callback_url'])
    session[:token] = access_token.token
    user_info(access_token)

    redirect_to accounts_path
  end

  private

    def user_info access_token
      @user_info ||= JSON.parse(access_token.get(ENV['oauth_path'] + '/api/v3/user').body)
      session[:name] = @user_info['name']
      session[:avatar] = @user_info['avatar_url']
      session[:admin] = @user_info['is_admin']
    end

    def client
      OAuth2::Client.new(
        ENV['client_key'],
        ENV['secret_key'],
        site: ENV['oauth_path']
      )
    end
end