How can I force SSL on a protected directory and prevent double authentication?

When you want to force SSL on a protected directory, if you don't taking special steps, a user who visits the protected directory using unsecured http will end up having to authenticate with the protected directory twice: the first time in unsecured cleartext, and then again after being redirected to the https secure URL.

AskApache has an article describing a good workaround for this problem.

Thanks to Jeff S. of Forerunner Ministries for the link!