Solution
You will need to delete the cookies for the authentication, so in Firefox (Linux) go to Preferences, remove individual cookies for the specific domain.

Solution

1. Install the act_as_authenticated plugin:

   script/plugin install http://svn.techno-weenie.net/projects/plugins/acts_as_authenticated

2. Generate controllers, models and migration:

   script/generate authenticated user account

3. Add necessary user foreign keys in appropriate tables (ie customer in xxx_create_users.rb), plus other fields you may want to use in your user table (ie role):

   create table "users", :force => true do |t|
     t.column :login, :string
     ...
     t.column :role, :string, :default => 'C'
     ...
     end
     add_column :customers, :user_id, :integer
     ...
     def self.down
       ...
       remove_column :customers, :user_id
     end

4. Run the migration:

   rake db:migrate VERSION=xxx

5. Comment out from app/controllers/account_controller.rb the following:

   include AuthenticatedSystem

6. Add it in the app/controllers/application.rb just under the class declaration.
7. Add in application.rb (same as above) the following just after the session section:

   before_filter :login_required, :except => [:login, :signup, :logout]

8. Comment out the default redirection after login and put your own (ie customers): in the account_controller.rb, just before
   the flash[:notice] = “Logged in successfully”.
   Also add the else for the the invalid login:

     redirect_back_or_default(:controller => 'customers', :action => 'list')
     flash[:notice] = "Logged in successfully"
   else
     flash[:notice] = "Invalid Login/Password!"

9. Change the action in the signup and logout functions in the account_controller.rb file from index to login
10. Add (optionally) more fields (role) in the signup page (app/views/account/signup.rhtml):

    
    User role
    
    <%= f.select :role, ['A','R','C'] %>

11. Add restrictions for displaying records depending on user logged in, by using the conditions_for_collection of the activescaffold plugin in app/controllers/customers_controller.rb:

    def conditions_for_collection
      ['customers.user_id = (?)', current_user.id]
    end

12. Add a menu page layout in app/views/layouts/_menu.rhtml:

    
      <% if logged_in? %>
        <% if current_user.role == 'C' %>
          <%= link_to "add user", :controller => "account", :action => "signup" %>   |
          <%= link_to "assign customer", :controller => "users", :action => "list" %>   |
          <%= link_to "change password", :controller => "account", :action => "change_password" %>   |
          <%= link_to "customers", :controller => "customers", :action => "list" %>   |
        <% end %>
        <%= link_to "logout", :controller => "account", :action => "logout" %>   |
        <%= "Logged in as " + current_user.login %>
      <% end %>

13. Add the call to the menu partial in the app/views/layouts/application.rhtml, just before the div with id=main :

    <%= render :partial => "layouts/menu"%>