brewery/app/controllers/sessions_controller.rb

class SessionsController < ApplicationController
  def new
  end

  def create
    user = User.find_by username: params[:username]
    if user.nil?
      redirect_to signin_path, notice: "User #{params[:username]} does not exist!"
    else
      session[:user_id] = user.id if user
      redirect_to user
    end
  end

  def destroy
    session[:user_id] = nil
    redirect_to "/"
  end
end