application_controller.rb

class ApplicationController < ActionController::Base

  protect_from_forgery

  # Need a way to use :except to ignore a specific controller (ie: MessagesController)

  before_filter :authenticate, :except => ["index"]

  private
  
    def authenticate
      authenticate_or_request_with_http_basic('Administration') do |username, password|
        username == 'admin' && password == 'password'
      end
    end
    
end

messages_controller.rb

class MessagesController < ApplicationController

  # this controller should not require HTTP Authentication
  
  skip_before_filter :authenticate
  
  def messages_inbound
    # do stuff here
  end

end

before_filter :authenticate, :except => ["index"]

private
def authenticate
http_basic_authenticate_with name:'xx', password:'yy'
end

you might need to change that to this:

def authenticate
authenticate_or_request_with_http_basic('Administration') do |username, password|
username == 'admin' && password == 'password'
end
end