admin_controller.rb

before_filter :authenticate_admin, :except => [:login, :login_verify]
  before_filter :save_login_state_admin, :only => [:login, :login_verify]

  def login
    # login form
  end

  def login_verify
    authorized_admin = Admin.authenticate(params[:admin_username], params[:admin_password])
    if authorized_admin
      session[:admin_id] = authorized_admin.id
      flash[:notice] = "Login Successful"
      flash[:color] = "success"
      redirect_to :action => 'dashboard'
    else
      flash[:notice] = "Invalid login. Please try again"
      flash[:color] = "error"
      render "login"
    end
  end

  def logout
    session[:admin_id] = nil
    redirect_to :action => 'login'
  end

application_controller.rb

protected
  def authenticate_user
    unless session[:user_id]
      redirect_to(:controller => 'account', :action => 'signin')
      return false
    else
      @current_user = User.find session[:user_id]
      return true
    end
  end

  def save_login_state
    if session[:user_id]
      redirect_to(:controller => 'account', :action => 'dashboard')
      return false
    else
      return true
    end
  end