Testing HTTP Digest Authentication in Rails

Rails 2.3 introduced HTTP Digest authentication to go along with HTTP Basic as simple ways to authenticate access to your application. HTTP Digest is more secure than Basic for several reasons. First, no passwords are transmitted in cleartext (Basic only Base64 encodes them — there is no encryption). Second, the content of the HTTP_AUTHORIZATION header is tied to a request method and URI. Third, there is a limited window of time an attacker could re-use the header in a replay attack even against the same request method and URI (five minutes in 2.3.2).

These are compelling reasons to switch to Digest from Basic, but there is one problem. How do you test it? For good test coverage, clearly you want to verify that actions that should be protected are, and that only valid username/password combinations permit access.

Basic is easy (in test_helper.rb):

def authenticate_with_http_basic(user = 'one', password = 'one')
  @request.env['HTTP_AUTHORIZATION'] = "Basic #{Base64.encode64("#{user}:#{password}")}"

Try this for Digest (outside of everything else in ActiveSupport::TestCase):

require 'digest/md5'
class ActionController::TestCase
  def authenticate_with_http_digest(user = 'admin', password = 'admin', realm = 'Application')
    unless ActionController::Base < ActionController::ProcessWithTest
      ActionController::Base.class_eval { include ActionController::ProcessWithTest }
    @controller.instance_eval %Q(
      alias real_process_with_test process_with_test
      def process_with_test(request, response)
        credentials = {
          :uri => request.env['REQUEST_URI'],
          :realm => "#{realm}",
          :username => "#{user}",
          :nonce => ActionController::HttpAuthentication::Digest.nonce,
          :opaque => ActionController::HttpAuthentication::Digest.opaque,
        request.env['HTTP_AUTHORIZATION'] = ActionController::HttpAuthentication::Digest.encode_credentials(
          request.request_method, credentials, "#{password}", false
        real_process_with_test(request, response)

Now, precede a call to get, post, put or delete with a call to authenticate_with_http_digest. The code above monkeypatches process_with_test to set up the proper HTTP_AUTHORIZATION header, but only for the current @controller, then runs the request normally.