def open_id_authentication(identity_url)
  # Pass optional :required and :optional keys to specify what sreg fields you want.
  # Be sure to yield registration, a third argument in the #authenticate_with_open_id block.
  authenticate_with_open_id(identity_url, 
      :optional => :nickname) do |status, identity_url, registration|
    case status
    when :missing
      failed_login "Sorry, the OpenID server couldn't be found"
    when :canceled
      failed_login "OpenID verification was canceled"
    when :failed
      failed_login "Sorry, the OpenID verification failed"
    when :successful
      if @current_user = @account.users.find_by_identity_url(identity_url)
        @current_user.nickname = registration["nickname"]
 
        if current_user.save
          successful_login
        else
          failed_login "Your OpenID profile registration failed: " +
            @current_user.errors.full_messages.to_sentence
        end
      else
        failed_login "Sorry, no user by that identity URL exists"
      end
    end
  end
end