Corporate CMS on .NET - what are the options?

There is an idea to remake our corporate website so that it goes with the times. The basic idea is something like an internal blog, which can be edited only from our internal network, but read-only from the Internet.

In this regard, user access should be controlled by Active Directory, and be invisible to users - so you have to use Mixed Mode Windows Authentication; the Internet should have a version in which there is no verification or ability to log in, and in which comments are not displayed, only topics. Such is the corporate Habr.

The main problem I encountered is that most free CMS work on PHP and MySQL, and our entire infrastructure is sharpened for IIS and MS SQL, and starting two more servers is not an option. Not because it is expensive, but in terms of support and availability. * Unfortunately, we don’t have NIX servers at all, and no one except me can work with Nix. The corporate site hangs on a fail-over Windows 2003 cluster, like the database server, and PHP has IIS, as far as I know, problems with this kind of clusters.
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Dozens of other projects and databases hang on the same servers, and somehow I don’t want to create a headache for myself by putting PHP on them - it turns out that there is a high probability of a fax.

So, we need a CMS that natively supports IIS .NET and MS SQL, and in which there is support for Mixed Mode Authentication, preferably embedded by developers, or at least in the form of a stable plug-in. Unfortunately, beta versions of plugins are not suitable for us due to possible security problems. It is desirable that it supports Windows Authentication and at the database level, but this is not so critical.

And of course, it would be cool to get all this for free, in the form of open source. Although, we will definitely compare them with paid ones, and we will decide on the basis of all available information.

So far, I have only found two systems, BlogEngine.Net and DotNetNuke , but both have problems with Windows Authentication.

It is interesting to find out if anyone has met a CMS that fits all of the above parameters?
What other rakes are when choosing?
And, of course, I would like to understand whether it is not easier for us to write what we need from scratch - what are the drawbacks of boxed systems, what bells and whistles can be useful for a corporate site (wiki, chat with a support group, ...), how flexible the rights users, and so on.

Thank you in advance!