# gemfile
gem 'bcrypt', '~> 3.1.7'

$ rails g model user name password_digest:text

# user.rb
has_secure_password
validates :name, :email, presence: true, length: { in: 2..255 }

$ rails g controller sessions new

# sessions controller.rb
class SessionsController < ApplicationController
def new
end
def create
  user = User.find_by(name: params[:name])
  if user && user.authenticate(params[:password])
    session[:user_id] = user.id
    redirect_to root_url
  else
    render :new
  end
end
def destroy
  session[:user_id] = nil
  redirect_to root_url
end
end

# sessions/new.html.erb
<h1>Login</h1>
<%= form_tag sessions_path do %>
<%= label_tag :name %>
<%= text_field_tag :name %>
<%= label_tag :password %>
<%= password_field_tag :password %>
<%= submit_tag "Log in" %>
<% end %>

$ rails g controller welcome index

# welcome_controller.rb
def index
end

# welcome/index.html.erb
<h1>Welcome</h1>

# application_controller.rb
def current_user
  if session[:user_id]
    current_user = User.find(session[:user_id])
  end
end
helper_method :current_user

# in the action controllers
before_action :authenticate_user

def authenticate_user
  redirect_to login_path unless current_user 
end