Why cancan not let me on the admin page?

Question

Ruby on Rails

Ability.rb:

class Ability
  include CanCan::Ability
    def initialize(user)
        user ||= User.new
        can :read, :all

        if user && user.role?(:admin)
            can :access, :rails_admin       # only allow admin users to access Rails Admin
            can :dashboard
            can :manage, :all
        elsif user.role?(:user)
            can [:read, :create], :all
            can [:update], Post, user_id: user.id
            can [:update, :destroy], Comment, user_id: user.id
            can :read, :all
        elsif user.role?(:moderator)
            can :manage, :all
        end
    end
end

rails_admin.rb:

RailsAdmin.config do |config|
  config.authorize_with :cancan
end

user.rb

class User < ActiveRecord::Base
  . . . . . .
  . . . . . .
  ROLES = %w[admin, moderator, user]

  def role?(requested_role)
    self.role == requested_role.to_s
  end
end

rails c:

irb(main):001:0> @user = User.first
irb(main):002:0> @user.role?(:admin)
=> true

When I try to log into /admin from under this user, it says You are not authorized to access this page.
How to fix?

Answer 1

Add config.authenticate_with in rails_admin.rb file

Answer 2

maybe you have a redirect from the /admin page that is not authorized to a page for which there is no access to
any mb device.