Summary

The article on Configuring Confluence with NTLM SSO is linking to an add-on that is no longer in service:

Confluence NTLM Authenticator

I'm not able to find it elsewhere, such as Marketplace.

In addition, it wasn't immediately obvious that this article is part of the Crowd documentation (and an outdated one at that). The only mentions of Crowd are in the breadcrumbs, the URL, and in the introduction.

See this Community post.

Suggested Solution

Either remove the document (as I've seen users mention this doesn't work with Confluence beyond 4.0) or update it with another solution that doesn't involve the no longer active add-on.